Best: Zack Fair from Crisis Core. He's sympathetic, yet optimistic, so if you're feeling despaired he'll lift your feelings back up. And being such a strong and fast warrior, he'll be able to catch food, defend you from dangers, and probably build a shelter or raft within an hour if he's got that giant sword of his (without it, two hours). And he's goofy so he'll be entertaining.
Worst: Marcus Fenix from Gears of War. He'd look around the island, roar, roll behind cover, and shoot your head off. Then he'd kneel face-first and eat your corpse. @_@