I was bored so I went to training mode and tried to find the strongest attack in each category save throws.
By "strength", I mean K.O. power. I haven't tested most damaging yet though in most cases most damage and most knockback overlap. I tested attacks on a dummy Mario from the middle of FD. Reducing knockback was accounted for.
Standing A - Snake's punch, punch, kick. The kick hits like a Smash attack.
F-tilt - Ike's horizontal slash. Stronger than many smash attacks.
A few other's such as Ganondorf's "Sparta Kick" and Zelda's magic hand slash thing come close.
U-tilt - Ganondorf's ax kick. Nigh impossible to land, but satisfying when it does.
Snake's broke a$$ up kick is probably the BEST up tilt, followed by a few other's such as DeDeDe's head butt and Zelda's magical slashy thing.
D-tilt - Ike's crouching slash.
F-smash - DeDeDe's crushing hammer of justice. Kills Mario uncharged from the middle of FD at about 50 frickin percent, but has the highest start up frames of any f-smash. Good luck landing it.
Ike's crushing slash, (which he stole from Smash 64's Link), is almost as strong and easier to land.
Snake's rpg comes third in this category.
U-smash - Ivysaur's spore burst. What Pokemon attack is that? Stun spore doesn't do damage as far as I remember.
Kills at like 60%. One of the few reason's to use Ivyasur if you ask me considering it's terrible recovery.
Lucas psychic burst thing comes second. That move is scary.
Ike's 180 degree slash is also very strong.
D-smash - Lucas' copy of Mewtwo's d-smash from Melee. I think it gets weaker with each burst. Too bad it only hits in one direction. Well it kinda hits behind you a LITTLE bit.
Ike's double slash is also worth mention.
Toon Link's single hit d-smash can kill at like 10% near the edge, but it's pretty much impossible to do on purpose.
Dash attack - DeDeDe's belly flop. Like his f-smash, phenomenally powerful, but very hard to land.
Snake's dive is probably the BEST dash attack, especially with Snake dashing.
Ganondorf's dash attack is also very good.
Glide attack - I never really tested this one, but it appears Charizard's is the strongest, and Metaknight's is the "best".
Nair - R.O.B.'s spinning flame. Not much argument here.
Snake's inflicts the most damage (28%).
Fair - Zelda's sweet spotted "lightning kick". I think it's harder to sweet spot in Brawl than in Melee, but it's still not that hard.
There are many other powerful fairs such as Ganondorf's crush punch, DK's double club, Mario's crush punch, and C.Falcon's now-impossible-to-sweet-spot knee.
I think Marth's is the "best".
Dair - Link's Sword Plant. Kills at 85%.
Ganondorf's murder stomp comes second, killing at 88%. Deadly spike, and spammable damage builder with auto-cancelling. Kinda odd how hitting him downward makes him bounce upward.
R.O.B., Ness, and Zelda also have good, reasonably easy to land spikes, though Zelda's you have to sweet spot.
I think Snake's is the most damaging (28%).
Bair - Zelda's reverse lightning kick.
Ganondorf, Ike, DeDeDe, Ness, R.O.B. and Snake have notable bairs as well.
Most agree that Game and Watch's turtle is the "best".
Uair - Zelda's magical flame burst thing.
Ivysaur's floating spore burst uair comes second.
Or maybe that's Ike's whirling overhead slash....
Peach, Snake and Ganondorf also have notable uairs.
Neutral B - Ike's Eruption. If you charge it up NEARLY all the way, it kills Mario off the top of FD at 10%.
If you charge it up ALL the way, then it will hit opponents laterally with less knockback, but more damage. You will also receive 10 damage. I'd say let it go a little early.
Ganondorf's Warlock Punch is second. Kills Mario from the middle of FD at 29 freaking percent.
The reverse kills at 23%.
Yes, it is stronger that Ike's fully charged Eruption.
Marth's aptly named Shield Breaker and the legendary FALCON PAUNCH!! are also notable.
Ness' PK Flash ties for most damaging with Ike's fully charged Eruption (37%).
EDIT: I was wrong here. I listed Warlock punch as the strongest when in fact it was partially charged Eruption. Thanks to Mystical Kenji for the tip.
Side B - Game & Watch's Judgment: 9. Hits like a Home Run Bat. Pretty much an instant kill from anywhere at a little more than zero.
Zelda's broke a$$ Din's Fire is probably the BEST if you ask me.
Marth's Dancing Blade is also great as it racks up damage and refreshes other moves.
Up B - Ness's PK Thunder Rush AKA Psycho Crusher. Kills at like 30%.
Luigi's SHORYUKEN! ( Fire Jump Punch) is second. Kills at like 50% and up. It works best if you yell SHORYUKEN! with every attempt. Guaranteed to get some laughs everytime.
Lucas' Psycho Crusher is also very powerful.
Metaknight's Shuttle Loop is probably the "best".
The best in terms of recovery would either be Pit's wings or R.O.B.s boosters.
EDIT: I was wrong. Ness's Psycho Crusher is in fact the strongest (kills at like 30%). But SHORYUKEN! is more fun...
Thanks to Earthbound 360 for the tip.
Down B - Game & Watch's full bucket (assuming you got three very powerful projectiles such as 3 super scopes, 3 Aura Spheres, 3 Charge beams etc). Hits for a phenomenal 60% and instant kills pretty much anyone from pretty much anywhere at pretty much any percentage. I never tested Ike's counter against this, but considering Ike's counter always inflicts 1.2 times the damage of the attack, I guess the counter to the full bucket would inflict 72%.
Jigglypuff's rest is also notable, even though the risk of a literally 3 second lag is NOT worth it, considering it has a ridiculously small hitbox and only kills at like 60% anyway.
DeDeDe's fully charged jet hammer is also deadly, though I noticed that it has the highest knockback if released just as the flame turns blue, but not when it starts to hurt you. While it's hurting you, it inflicts more damage when swung, but has less slightly less knockback.
Wario's Nuclear Fart is also powerful though it has surprisingly low knockback considering it takes like 2 minutes to charge. It actually has more knockback when it is charged 3/4 of the way (55 seconds). Thanx to Germanydabassist and Noobcake for the tip.
EDIT: Final Smash - Marth's Critical hit. Kills anyone from anywhere in one hit guaranteed (assuming your not playing in a "box" like custom stage.)
The most damaging is Olimar's End of Day which inflicts 97% if you land the whole thing. Thanx to Ilex for that tip.
The second most damaging is Link/Toon Link's Triforce Slash. Point blank, it inflicts 83%[/B ] damage.
EDIT: Item - Home Run Bat and Dragoon. Duh. Instant kill from zero.
EDIT: Assist Trophy - Isaac's psychic hand push. Can kill at zero, especially on stages with walk off edges.
Lil' Mac and Knuckle Joe have some extremely powerful uppercuts.
EDIT: Pokemon - Kyogre's Hydro Pump or Hydro Cannon or whatever it is. Can kill at zero. Hard to escape except for those characters with godly recovery.
Ho-oh's Sacred Fire is the most damaging (81%).
If you think the list is wrong, correct me, and I'll fix the OP. You can also add your own Superlative list of something else. A section on throws would be appreciated since I'm not about to add that myself.
By "strength", I mean K.O. power. I haven't tested most damaging yet though in most cases most damage and most knockback overlap. I tested attacks on a dummy Mario from the middle of FD. Reducing knockback was accounted for.
Standing A - Snake's punch, punch, kick. The kick hits like a Smash attack.
F-tilt - Ike's horizontal slash. Stronger than many smash attacks.
A few other's such as Ganondorf's "Sparta Kick" and Zelda's magic hand slash thing come close.
U-tilt - Ganondorf's ax kick. Nigh impossible to land, but satisfying when it does.
Snake's broke a$$ up kick is probably the BEST up tilt, followed by a few other's such as DeDeDe's head butt and Zelda's magical slashy thing.
D-tilt - Ike's crouching slash.
F-smash - DeDeDe's crushing hammer of justice. Kills Mario uncharged from the middle of FD at about 50 frickin percent, but has the highest start up frames of any f-smash. Good luck landing it.
Ike's crushing slash, (which he stole from Smash 64's Link), is almost as strong and easier to land.
Snake's rpg comes third in this category.
U-smash - Ivysaur's spore burst. What Pokemon attack is that? Stun spore doesn't do damage as far as I remember.
Kills at like 60%. One of the few reason's to use Ivyasur if you ask me considering it's terrible recovery.
Lucas psychic burst thing comes second. That move is scary.
Ike's 180 degree slash is also very strong.
D-smash - Lucas' copy of Mewtwo's d-smash from Melee. I think it gets weaker with each burst. Too bad it only hits in one direction. Well it kinda hits behind you a LITTLE bit.
Ike's double slash is also worth mention.
Toon Link's single hit d-smash can kill at like 10% near the edge, but it's pretty much impossible to do on purpose.
Dash attack - DeDeDe's belly flop. Like his f-smash, phenomenally powerful, but very hard to land.
Snake's dive is probably the BEST dash attack, especially with Snake dashing.
Ganondorf's dash attack is also very good.
Glide attack - I never really tested this one, but it appears Charizard's is the strongest, and Metaknight's is the "best".
Nair - R.O.B.'s spinning flame. Not much argument here.
Snake's inflicts the most damage (28%).
Fair - Zelda's sweet spotted "lightning kick". I think it's harder to sweet spot in Brawl than in Melee, but it's still not that hard.
There are many other powerful fairs such as Ganondorf's crush punch, DK's double club, Mario's crush punch, and C.Falcon's now-impossible-to-sweet-spot knee.
I think Marth's is the "best".
Dair - Link's Sword Plant. Kills at 85%.
Ganondorf's murder stomp comes second, killing at 88%. Deadly spike, and spammable damage builder with auto-cancelling. Kinda odd how hitting him downward makes him bounce upward.
R.O.B., Ness, and Zelda also have good, reasonably easy to land spikes, though Zelda's you have to sweet spot.
I think Snake's is the most damaging (28%).
Bair - Zelda's reverse lightning kick.
Ganondorf, Ike, DeDeDe, Ness, R.O.B. and Snake have notable bairs as well.
Most agree that Game and Watch's turtle is the "best".
Uair - Zelda's magical flame burst thing.
Ivysaur's floating spore burst uair comes second.
Or maybe that's Ike's whirling overhead slash....
Peach, Snake and Ganondorf also have notable uairs.
Neutral B - Ike's Eruption. If you charge it up NEARLY all the way, it kills Mario off the top of FD at 10%.
If you charge it up ALL the way, then it will hit opponents laterally with less knockback, but more damage. You will also receive 10 damage. I'd say let it go a little early.
Ganondorf's Warlock Punch is second. Kills Mario from the middle of FD at 29 freaking percent.
The reverse kills at 23%.
Yes, it is stronger that Ike's fully charged Eruption.
Marth's aptly named Shield Breaker and the legendary FALCON PAUNCH!! are also notable.
Ness' PK Flash ties for most damaging with Ike's fully charged Eruption (37%).
EDIT: I was wrong here. I listed Warlock punch as the strongest when in fact it was partially charged Eruption. Thanks to Mystical Kenji for the tip.
Side B - Game & Watch's Judgment: 9. Hits like a Home Run Bat. Pretty much an instant kill from anywhere at a little more than zero.
Zelda's broke a$$ Din's Fire is probably the BEST if you ask me.
Marth's Dancing Blade is also great as it racks up damage and refreshes other moves.
Up B - Ness's PK Thunder Rush AKA Psycho Crusher. Kills at like 30%.
Luigi's SHORYUKEN! ( Fire Jump Punch) is second. Kills at like 50% and up. It works best if you yell SHORYUKEN! with every attempt. Guaranteed to get some laughs everytime.
Lucas' Psycho Crusher is also very powerful.
Metaknight's Shuttle Loop is probably the "best".
The best in terms of recovery would either be Pit's wings or R.O.B.s boosters.
EDIT: I was wrong. Ness's Psycho Crusher is in fact the strongest (kills at like 30%). But SHORYUKEN! is more fun...
Thanks to Earthbound 360 for the tip.
Down B - Game & Watch's full bucket (assuming you got three very powerful projectiles such as 3 super scopes, 3 Aura Spheres, 3 Charge beams etc). Hits for a phenomenal 60% and instant kills pretty much anyone from pretty much anywhere at pretty much any percentage. I never tested Ike's counter against this, but considering Ike's counter always inflicts 1.2 times the damage of the attack, I guess the counter to the full bucket would inflict 72%.
Jigglypuff's rest is also notable, even though the risk of a literally 3 second lag is NOT worth it, considering it has a ridiculously small hitbox and only kills at like 60% anyway.
DeDeDe's fully charged jet hammer is also deadly, though I noticed that it has the highest knockback if released just as the flame turns blue, but not when it starts to hurt you. While it's hurting you, it inflicts more damage when swung, but has less slightly less knockback.
Wario's Nuclear Fart is also powerful though it has surprisingly low knockback considering it takes like 2 minutes to charge. It actually has more knockback when it is charged 3/4 of the way (55 seconds). Thanx to Germanydabassist and Noobcake for the tip.
EDIT: Final Smash - Marth's Critical hit. Kills anyone from anywhere in one hit guaranteed (assuming your not playing in a "box" like custom stage.)
The most damaging is Olimar's End of Day which inflicts 97% if you land the whole thing. Thanx to Ilex for that tip.
The second most damaging is Link/Toon Link's Triforce Slash. Point blank, it inflicts 83%[/B ] damage.
EDIT: Item - Home Run Bat and Dragoon. Duh. Instant kill from zero.
EDIT: Assist Trophy - Isaac's psychic hand push. Can kill at zero, especially on stages with walk off edges.
Lil' Mac and Knuckle Joe have some extremely powerful uppercuts.
EDIT: Pokemon - Kyogre's Hydro Pump or Hydro Cannon or whatever it is. Can kill at zero. Hard to escape except for those characters with godly recovery.
Ho-oh's Sacred Fire is the most damaging (81%).
If you think the list is wrong, correct me, and I'll fix the OP. You can also add your own Superlative list of something else. A section on throws would be appreciated since I'm not about to add that myself.