Honestly, I would have picked Cap and Winter Soldier v Iron Man.
To me, while not as epic as the airport fight it, it was more intense - as it was the most personal of all those fights. Unlike the airport fight, where they're not going all out, in that final fight Iron Man is trying to kill Bucky, and because it's been set up properly, we the audience don't blame him - and at the same time sympathize with Steve trying to protect his friend.
It's well done, well choreographed without looking like ballet and all in all has a lot of emotion behind it.
To me, that makes it the best. Sometimes epic battle scenes seem hollow, unless the stakes feel personal - and that comes down to set-up.
e.g. my favorite action scenes in the LOTR trilogy are
1) the fight in the mines of Moria (right through to Gandalf's fall), because we feel the fellowship's desperation, and we care about the characters. When Gandalf fell, people in the cinema I was in started crying.
2) The charge of the Rohirrim (in ROTK) Theoden gives that amazing speech, short and rousing, before they charge off to certain doom.
Sure, the scale of the 2nd scene is epic, but the set up really gets us engaged with the characters. I mean, if that doesn't happen then you really don't care who's punching who, and sadly there are plenty of movies out there like that.....