To use? Pikachu. In melee he's okay, but in Brawl he's almost overpowered. I mean, many characters are seemingly broken in that game, but Pikachu is just so bad ass. Many attacks cancel other attacks out, have huge range, and do good damage. A lot of the attacks don't even leave you that open after you use them. Her (it's a her, right?) skull bash used to make you stumble, but now she lands running after using it. You can recover from being thrown far away by spamming skull bash towards the platform, with quick attack at two good angles and you can almost always recover unless you are thrown out of bounds. She's also really fast. Her one flaw I find, is being a light character (not the lightest, mind you) so it's easy to get her out with a lower percent, and she has no spike attack. I can't spike people to hell like my friends can; I'm terrible at it with any character, so this is never a problem for me.
Pika-Pika-Pikachu!