ive heard strong arguements for both yoshi and bowser, but im going to have to go with yoshi, because one of the best yoshis in the world lives with me, and ive seen him put the smackdown on MK, ive seen him wavedash, and i saw him play seriously for the first time in a long time. yoshi is a lot like sonic, as a character, he is crap, but the ATs and mindgames that he can break out, make him a really solid character. and the learning curve is way steep to use him.
for the record,
yoshi can Down smash OOS, its basically his only option besides rolling, but its so good that it almost doesnt matter
and you can really punish a good yoshis grabs, they should be pivoting their grabs, it gives them the ability to have the grab range of D3 while doing a a fast grab with litttle recovery while running backwards, which gives added safety. its really too good,
its amasing (and kind of saddening as well) how characters like samus, tink, wolf, sonic and samus, have such awesome fun moves, but nobody barely ever gets to see them because even with all this cool stuff, they cant really do anything against shuttle loop and snake's f-tilt