I think tier lists go from best to worst; top, good, average, low, crap. Found the list. Seems I'm wrong. Anyway, since Pikmin were killed easily in the game, I can bet that they'll be easy to kill in Brawl with AOE (flame thrower and explosive type attacks) killing them even faster.
Top
1. Fox
2. Falco
Upper
3. Sheik
4. Marth
5. Peach
Middle
6. Captain Falcon
7. Ice Climbers
8. Samus
9. Dr. Mario
10. Jigglypuff
11. Mario
12. Ganondorf
Low
13. Link
14. Luigi
15. Donkey Kong
16. Roy
17. Young Link
18. Pikachu
Bottom
19. Yoshi
20. Zelda
21. Mr. Game & Watch
22. Ness
23. Bowser
24. Kirby
25. Pichu
26. Mewtwo