Jacob, hands-down. While being sweet, relatively intelligent/thoughtful, and kind most of the time, he also has his somewhat arrogant and petty side. And I'd be thankful for that. They're clear flaws that really make him human (and werewolves are just really cool, IMO). I don't think I'd be able to survive a single month with Edward, and not just because he's a flesh-eating vampire. =P I just find him sort of self-righteous and overprotective, yet nonetheless portrayed as a little too perfect. It seems to me that Jacob is protective while not being intrusive, ie, a genuinely caring and compassionate side that DOESN'T manifest itself in "Stay away from me, I might kill you at any second!" He has faith in himself and in Bella, even though she often doesn't really deserve it, though he's not exactly forgiving all the time. He'd just be easy to live with, easy to talk to, not overly angsty... everything Edward isn't.
Team Jacob. *raises fist*
*waits for the onslaught of screaming Edward fangirls*
...Romantic preferences aside, I also like Carlisle. He's got a sense of clarity, wisdom, and integrity that exceeds all other characters in the books. He actually has enough perspective to see things for what they are and take all things into account on an impartial point of view, which is admirable in this case.
Seth also just strikes me as sort of Jacob-y, except with more of the sweetness and innocence. He's a little less mature, but he's still a nice guy. <3 And to add someone who's not a guy, for the sake of variety, I'd have to say Leah. She has a caring side but she can actually sense when the time is right to knock some sense into people who need it, and while she has her immature, dramatic, self-serving side, it's not without reason. She has genuine motives that are actually realistic. She and Jacob are the two most realistic characters in the books, even though SM sometimes seems determined to cast them in a bad light. (Like when they act like brats over Bella. That could be seen as an attempt on their lives.)