So I feel like within each group of tiers, there are smaller groups within them (ala the Brawl tier list). When looked at this way, I feel that things make a little more sense. I also consider how relevant the character is today.
High Mid Low
Top (Defines the metagame):
1. Fox - A lot of really good options. Fast, decent recovery, good combos, shine.
2. Falco - The only reason he's lower than Fox is his recovery.
3. Marth - Excellent spacing, has an easier time dealing with spacies, and more of an overall prominence in the meta.
4. Sheik - Long tech chases, chain grabs, good punish game. Less of a prominence than Marth, but still good.
5. Jigglypuff - Best recovery in the game, rest, amazing off stage game, long aerial strings, less of a prominence.
6. Peach - Tricky movement, turnips (with OP luck chance), good aerials, lives a long time.
7. Ice Climbers - Excellent ground game, wobbling, gets beat out by shine, way more relevant recently.
8. Captain Falcon - Fast, good punish game, knee, bad recovery, less prominence within the top players.
Mid Tier (Requires more technicalities to be successful):
9. Pikachu - Axe pushing the character to the point where he's a hair away from being a God is enough to justify this spot.
10. Samus - Great recovery, great zoning, but there is no player as good as Axe to justify her being higher than Pika.
11. Luigi - Fast ground speed, very floaty, bad recovery, a lot more relevant recently. Room to grow.
12. Doc - Lacks recovery, approach options, and prominence in the meta, but good at everything else.
13. Mario - The only reason he's lower than Doc is due to lack of proof that makes him better than Doc. Has potential.
14. Yoshi - Unorthodox, but viable. Once aMSa has won enough sets against the Gods, I'll consider Yoshi to be higher.
15. Ganondorf - Hits really hard, kills early, decent spacing, slow, meh recovery, relevant.
Almost Viable (Has the potential to be Mid Tier, but has too many shortcomings or not enough proof to be in Mid Tier):
16. Young Link - Good movement and projectiles, but situational. Better as a secondary than a main unless proven otherwise.
17. Link - Same as Young Link, but slower, stronger, more range, and can hold his own. Not enough proof/relevancy.
18. Donkey Kong - Green Ranger proves him to be higher than everyone below, but lower than everyone above.
Not Vialbe (I think you get the point):
19. Mewtwo - Good recovery, floaty, interesting gimmicks, but bad at everything else.
20. Game & Watch - Game design flaws hinder him from being in the Almost Viable tier.
21. Zelda - Floaty, good recovery, kicks do a lot of damage, not many options.
22. Roy - The same reasoning as DK, except there is no good Roy player.
23. Ness - Interesting movement, lacks range, laggy specials, bad recovery.
24. Bowser - DJ Nintendo is the only person keeping Bowser relevant, combo food, can land a good read.
25. Kirby - TripleR is the only person keeping Kirby somewhat relevant. Good up air.
26. Pichu - Who mains Pichu?