Marth. Definitely Marth.
His sword, speed, and quick rolling ability all make him quite formidable, when played with well.
The only problem I have with him is his low traction. I often find myself correcting this problem by jumping more often, as opposed to an out-right change of direction on the ground. Some may argue his triple jump wanes in its ability to save him, however, there are other ways to get back to the edge, which makes his return quite useful.
Oh, and let's keep our egos in check. Far too often have I read "No one can beat me," and Jon, I'm not referring only to you, nor only this topic. It's just quite irritating reading such pompous remarks.