Wow, tough one. Picard is awesome, Worf would be a good choice, as would Garak of course, but my all time favourite would have to be Q(John de Lancie).
Why? Well, who can really explain Q? My favourite part is when he becomes mortal and says it's something wrong with his stomach because it hurts He possesses the same curiosity which star trek stands for, and that could be why he gets my vote.
A contract is a contract...(but only between Ferengi).