Who would it be? I would personally pick Wheatley from Portal 2. While kinda a screw-up, he's frickin hilarious.
Edit: Just to clarify, I meant like an artificial intelligence, a machine.
Edit: Cortana seems to be the favorite here (no surprise).
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Edited by Doc Bacon: 9/11/2015 4:38:41 AMElizabeth from bioshock infinite. Easy. Second would be Louis from L4D. Guy is always so cheery, he'd make the whole trip fun.