Hm... Will Smith of James Marsters? Tough choice, as I think they'd both be charming. But I'll go with JM, celebrity loyalty and all.

Just to add, when I think about that it's cool that he has those two people in mind, because so many movies are written with the pre-set assumption that the character will be white or black and that affects the casting... it's cool if he imagines his own character could be played either way. Though, I haven't read the books, so I imagine he does describe the character one way or another.