Most wanted:
1 > Mewtwo. I can see why some people don't want him because Charizard already fulfils the role of a popular gen I that can Mega-Evolve but asides from that, I think than Charizard and Mewtwo can have different roles as Smash Bros. playable characters and are completely compatible in the same game. Let's not forget than a lot of veterans are in SSB4 more because of their role in previous Smash instalments than because of their revelancy in current Nintendo universe. And Charizard in SSB4 is actually more a legacy from SSBB Pokémon Trainer than anything else, though I admit than the Mega Evolution greatly helped him to not be cut, an I highly doubt than Ivysaur an Squirtle are back because contrary to Charizard really they're only relevant as a Pokémon Trainer's Pokémon.
Of all SSBM characters that were cut in SSBB, I feel than Mewtwo is really the only character with any chance of being playable in SSB4, and it's the perfect time to get a SSBM cut as playable character again:
- The opportunity is and will probably be absolutely unique in the Smash history. I really don't see any character cut to go back in Smash 5 if the fourth instalment doesn't have a returning cut character.
- Contrary to other Melee cut, Mewtwo isn't a clone of any other SSB character.
- Mewtwo represents something other Pokémon confirmed as playable in Smash 4 can't do. He represents legendary Pokémon, an important concept in Pokémon universe that deserves representation IMO. Mewtwo is easily one of the most recognizable legendary Pokémon and a perfect representation for them.
- Mewtwo is now more relevant than before SSBB in Pokémon universe. He got a signature move, then a new movie, he teased Mega Evolutions and got TWO of them, is catchable in Pokémon X and Y and is even in Kalos regional Pokédex.
With all those arguments I think than it's the absolutely perfect time to get back a character cut from SSBM as playable in SSB4, and Mewtwo not returning back would heavily disappoint me for all those reasons. Also both Roy and Mewtwo were planned for SSBB, and while obviously Roy is not returning back I see Lucina as Roy's spiritual successor due to, just like him, being a Marth clone, even though that wasn't said officially by Sakurai. But contrary to Roy, Mewtwo is not a clone of anyone else and is actually relevant in recent Nintendo history. Just rework him to be better an he would be the very best addition to SSB4 IMO.
By the way, the detractors's arguments "Six Pokémon would be overkill if we count Jigglypuff" or "There were six Pokémon characters in Brawl because of Pokémon Trainer" aren't enough to convince me. Fire Emblem already surprised us with a total of four reps, and if six Pokémon reps, meaning probably more than Mario, can legitimately seem unlikely for some people, I personally highly doubt than Sakurai would not include Mewtwo as a playable character for the sole or primary reason than "there are already too many Pokémon characters".
2 > Isaac. Even though I never touched a Golden Sun game I think than Isaac is a very charismatic character and, according to what I read, with a lot of moveset potential. We really need more magic attackers in Smash Bros. because Zelda, Palutena and Robin (and Rosalina to a lessser extent) are not enough IMO. He's obviously the most recognizable character from Golden Sun and this franchise would be probably the best way to represent the Game Boy Advance era, just like how Olimar represents the GameCube era. Plus he got a third game after Brawl; even if it wasn't as great as the GBA games (again, according to what I read) it's still enough to give him post-Brawl revelancy.
3 > Fourth Starfox character. The real problem about this one is than this series doesn't have any post-Brawl revelancy, but still I imagine this franchise getting a fourth rep for some reason. First, we really need another series to get exactly four playable characters; even with Fire Emblem: Awakening being a great commercial succes for the standards of its series, this doesn't justify it for being the only franchise with exactly four reps IMO, even with Lucina being a late and lucky addition according to Sakurai. Second, a new Starfox game has been confirmed for the Wii U, and even if it will be released after SSB4, I really see Starfox getting the same treatment as Fire Emblem in Melee: we need to promote a game with Smash Bros. so we will give a series more representation than it deserves and in the future we will say « Smash Bros. saved the series from being ignored ». But I don't think that this potential newcommer will be one that doesn't exist currently and will debut in Starfox Wii U, really an already existent fourth rep like Krystal seems fine to make more people interested in the franchise.
4 > Ridley (non-Other M design). At this point I'm really confident about Ridley's chances as a playable character in SSB4. Not only Metroid deserves better representation but given Ridley's teasing my theory is than there is actually a stage boss on Pyrosphere, but that Ridley is not that stage boss, that will be something like Vorash or Goyagma instead. Any other possibility, in my opinion, can pretty much only be trolling, and not a cute or funny one like Sakurai is used to, but a literally bullcrap trolling: either he reveals a highly requested character as a downgraded version of the role he already played in Brawl after leaving volontarily his status unclear for months, or Ridley is actually playable but we don't have any boss on Pyrosphere; in either case, all that teasing would literally go to waste.
I'm not personally attached to Ridley, but I think he wouldn't have much problem to be unique, as a character with mostly aerial gameplay. I have little experience with Metroid, so I can't really imagine a moveset myself. But the funniest part would be the reveal trailer: imagine a scene at the end, after the "Super Smash Bros. for Nintendo 3DS / for Wii U" logo, where Ridley triumphed against Samus, then a sentence appears "No matter how big you may be, there is always someone bigger." and Ridley is attacked by the actual Pyrosphere boss. That would be hilarious.
5 > Magikarp. Obviously it's a joke want and I don't take it seriously, but seing Magikarp as the ultimate troll character in Smash would be absolutely hilarious, and only for this it deserves to be in my top want. The few moves it learns in Pokémon games would actually provide a decent moveset: Splash doesn't do damages but makes enemies tripping; Tackle would be similar to Diddy Kong's side-B besides the fact than it causes knockback instead if grabbing; Bounce is similar to Dedede's up-U but is faster; Flail works on a similar manner than Yoshi's down-B but has power based on the vertical distance you fall before hitting the ground. Its gameplay would be mostly based on aerial combos, with very weak damaging and knockout power but very fast an spammable attacks. Its final smash would be a Flail at full power (like when Flail is used at only 1 HP remaining in Pokémon games), with incredible damaging potential and more than decent knockout power.
Also imagine this priceless screen KO! Just for it I'd like to see Magikarp as a Smash playable character.
Again, it's a joke want, so don't take it seriously xD
Least wanted:
Can't think of a fifth.
4 > Chorus men / Chorus kids. Actually I'm fine with the idea of a Rythm Heaven rep and it would be a cool addition to the roster with a rythm-based gimmick, but please no Ice Climbers-like gimmick with three characters, with or without the rythm gimmick. Someone like Marshal alone would be better implemented in Smash Bros. IMO.
3 > Sceptile (or any other Grass starter for that matter). I don't feel than a Grass-type rep is necessary at this point. Sure, we have Charizard and Greninja, but those were implemented for other reasons than being starters. As said in Mewtwo's paragraph, Charizard is more of a Pokémon Trainer legacy than anything else. Greninja is in because according to what he said, Sakurai wanted a sixth gen Pokémon to be a playable character in SSB4 and choosen him because he immediatly loved his design. Neither seem to be chosen because of their type of because they're starters; for those reasons, a Grass starter to complete the trio feels unnecessary in my opinion. Also Sceptile supporters point the fact than he's perfect to represent Omega Ruby and Alpha Sapphire in addition to being a Grass-type starter rep, but those games are completely irrelevant to SSB4 IMO. Not only they release after SSB4 but, contrary to franchises like Starfox, or Fire Emblem during Melee times, upcoming Pokémon doesn't need to be promoted. At all. Omega Ruby and Alpha Sapphire will be a commercial success, it's pretty much set in stone, there is no point to promote them in another game.
In addition, the starter trio was actually relevant in SSBB because all the starters could transform into another one during battle, and they're all from the same generation. Plus I think than characters should be based on their own merits before anything else, so I hardly imagine Sakurai reasonning like "Oh we have a Fire and a Water starter, okay then I'll add a Grass-type one for the sake of completing the trio".
2 > Ridley (Other M design). As I already explained, I don't want to see Ridley deconfirmed because I don't want to see all this teasing to go to waste. If Sakurai planned to include Ridley as a stage boss and teases him with blatantly unclear status before deconfirming him, then Sakurai's trolling becomes worthless and not funny anymore. But on the other hand, I don't want to see Ridley as a playable character stuck on his Other M design. I don't like it at all, it doesn't do justice to Ridley IMO, other Ridley designs are much cooler. Unfortunately it seems to be the most likely design due to Other M being the most recent Metroid game, but I still hope than other designs will be alternate costume, even if I think it's compromised due to possible hitbox problems.
1 > Audino. I know that it doesn't have any chance to be actually playable but if by some miracle it ends up as a playable character that would kill all my hype for SSB4. Really I think than it's the only Nintendo character or creature I legitimately detest, both for its horrible design and role in Pokémon games (existence aimed at being an experience punching-ball in almost all Unova rustling grass or even Kalos Battle Chateau ? seriously ?!). Really if there isn't any sign of Audino in SSB4 not even as just a trophy that would be awesome for me.