Personally, I feel like it really actually breaks down into smaller groups then just the tiers. I think that generally characters are really close on each of these levels, and the current tiers are a bit large, in that not all the characters are of the same viability in each tier. Not all are the same here either, but it's much closer.
How I'd rank it:
















:shiek:








Meta Knight- kinda obvious, he has his own level because he is a level above everyone else.
Snake, Diddy, Falco- these 3 playing catchup with metaknight, they are all close (to each other)
Wario, Marth, Ice Climbers- these 3 round out top tier, all good, close on the heels of the preceding 3.
Olimar, Pikachu, Lucario- these 3 are borderline, they aren't always viable like top tier and have more struggles and flaws, while still being great.
ZSS, Tlink, Pit- these 3 mark the beginnings of upper tier, characters who can be viable but you have to work more then with top tier.
D3, G&W, Kirby, R.O.B.- these 4 are the falling stars of old, with staling metagames, their simple play hasn't advanced much, they make up the middle of upper tier.
Peach, Fox, Luigi, DK- these 4 are borderline on middle tier, you're gonna have to work with them, but they all are viable and can do well. Close to being upper tier, just not quite.
Wolf, Sonic, Sheik, PT- these 4 are the meat of middle tier, and can still do well in tournaments, but they are definitely mid tier and going to have to fight for it.
Ike, Ness, Lucas- these 3 mark the beginnings of low tier, good, but just not at that same level.
Bowser, Yoshi, Mario- the rest of low tier, the mushroom kingdom residents of old.
Falcon, Samus, Jiggly- the top of bottom tier, doesn't really say much I suppose.
Link, Ganon, Zelda- the bottom of bottom tier, the hyrule kingdom is laughed at.
EDIT: moved DK from low tier to mid tier, dropped D3 from top tier to upper tier.