There have been nice instances of decent duels, but personally for me nothing stands out in my mind. I did like Cap/Batroc in TWS, but it was short and sweet. Thor/Iron Man was....cute, I guess, but makes Iron Man look incredibly good, considering Cap and Bucky (two considerably weaker guys than Thor) were taking it to Tony in Civil War and caused plenty of damage (mind you, an incredibly vengeful Tony).
I don't want to sound like I have sour grapes, because if it's a team movie (or an ensemble cast like Civil War) I get that you can't focus in on one particular duel between two characters.