1. Jigglypuff - When you get KO'd by it and it taunts, that is SO annoying! Plus, it's only known for the anime appearance. Lastly, it's been wasting a slot in 3 games that another Pokemon (like a retooled Mewtwo could use)
2. Pichu-For some reason, Pichu doesn't annoy me as much, I guess because I can fall back on its cooler evolution.
3.-Young/Toon Link- In the SSB series, if you've played one Link, you've played them all. The only differences are size, knockback, damage, etc. I'd like new, innovative characters to replace the clones. I'd rather have a brand-new moveset than a slightly different one...
4. Falco/Wolf, Lucas- same as #3 above. However, I've heard that Wolf is a semi-clone, so I have to wait until I play Brawl to be sure (still waiting!

) Falco, IMO, is basically a Luigi-fied Fox. And Lucas is a Ness clone wasting space (except for PK Freeze).
5. Jigglypuff. AGAIN. I hate that thing with a passion. Wigglytuff's perfectly fine, especially since it didn't waste character slots. But Jigglypuff...I mean, Mewtwo has been more important than that thing since the start of Pokemon! Even before the anime, it attained Legendary (and broken-in-terms-of-power) status back in the Pokemon Red & Blue days! I really wanted a Mewtwo vs. Lucario scenario in Brawl, and the Puff ruined it! Well, here's hoping for Mewtwo's return in SSB4 (and hopefully the axing of Jigglypuff, however, no offense intended to its fans. Only offense towards Jiggly).
Honorable Mentions - Ganondorf, IF they're gonna continue his current CF-ish moveset. As of now, basically another clone wasting space, save for a few new Brawl moves/animations. Ganon, you have a sword. USE IT! Stop showing it at the end of the battle, because you'll regret it each time you lose a SSBM/SSBB battle.
I'd criticize Roy, too, but he was my 2nd fave swordsman in Melee

, and pawns Marth due to fire and having a 1-Hit KO (provided you have enough time and you have 3-4 people playing). Fire FTW! Anyway, I can absolutely settle for only Marth from now on, but I wish Roy was an Assist Trophy... He'll be missed, but I'm glad Ike carries his legacy!
So, all clones should have never existed (save for SSB 64 Luigi because he's key to Nintendo history), and Jigglypuff should've been replaced with Mewtwo. And BODY-wise, even Jiggly's a clone of Kirby...