Peach, Sonic, and Snake.
Peach: I didn't know I was any good with peach, until I randomly chose her-- and started winning EVERY match. Now I'm quite good with her.
Sonic: I started brawl expecting to hate sonic. From videos he looked too light/fast, and I didn't think sonic fit in very well... He was another suprise. I kick ASS with sonic n__n
Snake: Snake owns, no question asked. MGS series is my favorite game series, and I knew I would like/be good with snake.
My other best characters are Ike, Toon Link, and Wolf.