Out of the list? Gordan Freeman, I want that gravity gun.
But if I could pick anything else I'd have to say Doctor Wily from the Megaman games.
Giant Robots? Cool flying machine? Hundreds of Bosses at my complete control? I wouldn't even need to fight!
Count me in, as fun times are to be had!
Although there is the problem of Megaman showing up...but, since I am not bound by video game villian laws, I'll just send all the Bosses at him at simultaniously. Problem solved.
EDIT: ok, ok. If I did have to fight, I'd want to fight like Nightmare from Soul Calibur.
Also, his armor is incredibly kick-ass.