Damn, I was going to say BFR for the easy win for Strange, but this is harder.
Spoiler:
Both now have really good defense and offense, and can go airborne. I want to say Tony because if he actually connects, Strange is toast, whereas we see that Tony's armour can repair damage (though it does appear to have limits, as Thanos repeatedly damaged it to the point where it stopped repairing at the end). Still, I would give Tony a bigger chance of surviving Strange's attacks than the other way around.Strange's defense is no joke though. Between the massively upgraded shields and his ability to warp incoming attacks (as shown during his fight against Thanos), or redirect them with portals (as shown against Maw), as well as the cloak defending him, he is not that easy to connect cleanly. And those eldritch lightning arcs he used against Thanos looked pretty potent, at least based on how they were tearing up the landscape as well.