With prep time? Bruce is way smarter than Tony. He'd hack all his personal files, build his own suit, then use his superior intellect and combat skills to mop the floor with Iron Man. Tony is too proud to think he'd need to prep for "Some guy that dresses as a bat." Without a suit he'd simply hack Tony's suit and shut it down. Or build something that would fry it and shut it down. I'm not saying Iron Man wouldn't hold his own for awhile, but in the end Batman is still the superior intellect and tactician. If Batman knew nothing about Tony's suit and had no prep time? Ironman would have the edge since his suit is almost indestructible compared to most things Batman uses. But if Batman knew he couldn't win he'd easily be able to escape and buy some time until he could figure something out, and since Tony wouldn't kill him, Batman would be able to get away. Idk, it'd be a good fight for sure, but winning would be situational. In a battle of strength, Ironman would have the edge and probably win. In a battle of wits, Batman would win. The better question is; Batman vs Captain America. No prep time, thy just meet on the street and start fighting. That would be a good fight.