I think the format of the story is solidly going Sci-Fi, so use Spock--and if they've got some sort of Holo-deck maybe we can see some cameos from the other three (since the aliens seem acquainted with them already...and hopefully their version of Conan doesn't take it personally that he's not in the lead on the vote!)
Beatrix Kiddo. You don't want a guy as a sidekick. And I don't know who that other chick is, as I've never watched that show. Spock would probably be fun... for about 5 seconds. Conan... Somehow I picture Schwarzenegger's Conan, and imagine getting all my advice from him for a lengthy adventure. Not a fun thought. So Kiddo it is. Sexy, smart, deadly as hell... Nuff said.