I say Dexter wins on account of being a way better show. I tried to get into Hannibal but the show always felt like it was trying to be more clever than it actually was. Plus Will's whole empathetic deal felt like a borderline superpower that was written in so they could solve shit.
I want to say Graham given his feats but we saw he has trouble reading people who aren't psychopaths. Dexter while he is a psychopath is different from the norm as was pointed out by Vogel. Even after studying them for a life time she had trouble reading Dexter. This may throw Graham off the scent.