Top 10 (no order)
Marth
Fox
Sheik
Falco
Peach
Squirtle
Kirby
Pikachu
Luigi
MK
lol @ melee top tier. But yeah, Marth's range/power is a threat as always. Fox and Sheik are combo beasts. Falco retains an amazing control game and is now also a decent combo-er. Peach barely makes the list, but she defintely has good combos with instant float + no lag on aerials. Squirtle, Kirby, Pikachu, and Luigi are all crazy combo beasts with better than average recoveries. MK is still just amazing.
I think ZSS almost beats out Peach, but is just short. Her u-air is so sick and dthrow is amazing if you can land a grab.
Personally, I think a top 5 and bottom 5 would be more interesting, and helpful to those looking to balance the game. In that case I would have to say
Top 5 (no order):
Marth
Kirby
Squirtle
Shiek
MK
Bottom 5 (no order):
Bowser
Yoshi
Ness
Ivysaur
Snake
The tops I already mentioned above. As for the Bottom 5: Bowser is just too easy to juggle and has a blind spot underneath him. This combination is just sad for him. Yoshi has some combos, but he also has difficulty approaching AND is not too good at camping, so I'm not really sure what he should do. Ness still has his recovery and piss poor range. Ivysaur is still too easy to gimp and has very few effective strategies after you learn how to DI a bit. Snake just feels bad to me, with his tendancy to get combo'd and poor recovery.
I haven't really met any dedicated players of these characters though, so i could be wrong, but that is my opinion at the moment.