Oh? Only Prime? Hmmm I still say the Omnidroid takes him. That droid was freaking crazy man. Optimus is still organic metal... he didn't show any crazy strength, although his blasts and stuff might be effective, bu the omnidroid had access to a lot of weapons, and he was way faster and more agile than Prime too, not to mention the Omnidroid adapts to it's opponents.
Ohhhhhhhhhh well Iron Man and War Machine would only be flies bothering him he'd have to focus on Prime. If he does that he'd win. War Machine and Iron man didn't have any crazy strength feats and the Omnidroid can withstand military weaponry so I don't see how they do anything. Prime could use them as human shields or something.