I voted for Banjo. It was a toss-up between him and K. Rool, as I've wanted K. Rool in Smash for years, but in light of Phil Spencer's comments and Nintendo managing to strike a deal with Microsoft to get DK64 on Virtual Console complete with Jetpac, I think it's actually possible. And given the choice, Banjo would be so much cooler.
I don't know why so many people are voting for Wonder Red. The whole point of Wonderful 101 is that all members unite to become incredibly powerful. Individually, they're weak. The parts where you play as just Wonder Red in Wonderful 101 give you just a basic punch combo, and nothing else. Teaming up with others wouldn't work, as he couldn't fight alongside huge amounts of characters on the screen at once (outside of a Final Smash), and while they made Olimar work, that's because Pikmin are still used individually. All of the attacks in Wonderful 101 call for many members at once. Having a fist/weapon just appear in front of Wonder Red, or made up of only 1 or 2 members would not only look wrong (they're supposed to be many times the size of Wonder Red), but it would undermine the whole premise of Wonderful 101.
Wonder Red brings sizing issues that make Ridley seem trivial by comparison.