I got Sonic recently and used him to get a good feel. He's definitely an advance character and should probably only be used for the one-on-one.
Olimar is probably the most underestimated by people who think him as nothing because of his appearance and Pikmin. Ike is pretty decent, but i'll stick to Marth. Of the three Starfoxes, i think i'll still keep w/ Fox. I still haven't gotten Wolf yet.
Kirby is my homey, though. I dominate so much that it's hilarious. And i don't spam Down B. But i am a tad predictable when using it. Lnk is asn't n00by as before. His Up B is slower and you'll need more skill if you want to win w/ him. The character i hate the most is Game & Watch. Especially is acursed final smash. gahhh!!!!
I still haven't finished SSE co-op (HARD difficulty.) It's pretty decent so far, but i still got a long way to go.
The smash ball adds a new dynamic to the game. But some of the characters are the most cheaterous. Marth's sucks; Kirby's is awesome; Sonic and G&W are just plain cheaterous. But i hardly get the ball. I'm not that good at getting it.
EDIT: CPO, you're gonna get jumped. >;)

"...You might think I'm losing my mind, but I will shy away from the specifics..."