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 Savathûn: 6/14/2015 5:23:00 AMHonestly, the Ghosts from Destiny. They can do everything Cortana can, AND apparently resurrect the dead and imbue them with inhuman power.