Raphael, mainly because I like Sais.
Second place is Leondardo, because katanas are awesome... actaully now that I think about it, Michelangelo, Donatello, and Leondardo are pretty much even when it comes to me liking them, and none of them are very far behind Raphael.
Ignore all of that, while my official answer is Raphael because of his weapons, more side answer is that I like them all because they are all awesome.