Sanji.
Reason One: Best fighting style ever. Kicks make for the best moves around, and seeing somebody who fights with nothing else really impresses me.
Reason Two: Style. Sanji has it in spades. Everything he does; his clothes, his words, his actions, they all shout out "Class!" in a way I've yet to see in any other character for anything, period. Also, I abhor smoking…. but Sanji makes it cool. I'm not saying smoking makes Sanji cool, I'm saying the other way around... Sanji is just so awesome he makes even smoking seem cool. But (insert anti-smoking ad here so I don't get yelled at.)
Reason Three: The gentleman. Sanji is the epitome of the gentleman. It's true he's a flirt, some might say a perv, and girls are his driving force... might be, but that doesn't change the fact that he really is a gentleman and a suave guy, despite that.
Reason Four: Interesting moments. His interactions with any other character will provide amusement. Watch him goggle over Nami, Vivi, and Robin! Watch the fights over food with Luffy, the comradie/irritated moments with Usopp, the constant fighting with Zoro...
Reason Five: The dream. Out of all the dreams possessed by the Straw Hats, I find Sanji's to be... well, perhaps not the most noble of them all, but definately the most unique. It's also the most interesting dream, to me. It's not to become anything, or to do some great task... it's to find a place he's always wanted to see, despite the uncertainties of its existance. A man chasing the dreams of his childhood, with a sparkle in his eye. That is Sanji's dream...
So, did I explain my vote well enough? ;p