The last one - with aquatic features, rollers and a gun - is flawless to me. he embodies most of things I enjoy in fictional avatars: Rollers = speed and movement, gun user = shooting expert (add speed to that and he's unstopabble), and aquatic-like features = I love water animals. Seriously he's perfect.
Him aside, Bubble Girl and the other green design are also fairly amazing imo. It IS a shame they were unused. Hey, maybe they'd be great material to use in some sort of well-written fanfiction! I'd love to do that. Can we like think up some names and backstories for those guys?