Hmm, I have to admit that it has to be L, considering he knew pretty much from the start of the series that Light was Kira; he just didn't have the proof to back it up for us common folk. Light was just too obvious with all the risks he took for him. As for Lelouch, he probably falls somewhere in between, with the fact that he went through all he did knowing it's for Nunally, when he should've known that his purpose was his weakness pulling him down.

Taking GAR into account, though, it's anybody's win.