1. Blue Yoshi
Yoshi is just plain awesome in brawl. His attacks are quite quick. I also tend to prefer jumping attacks, and Yoshi does a good job of that.
2.Green Pokemon Trainer
His three pokemon are pretty good for brawl, in my opinion. A good way to go with him is to start with Squirtle and his fast attacks, switch to Ivysaur for some quick attacks, then go to Chaizard to finish your opponents off. (or just go all Charizard, that works well for me). Also, why green? Look at green Charizard, look to the left, and you'll see why.
3. (this is a hard pick) I really don't have a third main, because it is at this level that I just pick certain other characters at about the same time. they include (in no particular order): Mario, Link, Pikachu, Samus, Ike, and Wario every so often.