I like the Captain America trilogy, but it's one I like less the more I go back to it. It's certainly far from bad, but I find them less enjoyable every time. First Avenger has become a bit of a slog to go back to for me, and though I enjoy it, it's mainly just for Chris Evans and Hayley Atwell. Winter Soldier I think is probably the best made in the trilogy for the first two acts, but I think it shoots it's attempts at social commentary in the foot, and the third act I find rather dull. Civil War I like a lot. It's my favourite of them as, though it's probably less well made than the first two acts of Winter Soldier, it doesn't annoy me by attempting social commentary and criticisms of mass surveillance and then ducking out with "oh it's fine, the evil Nazis did it." It also, in my opinion, has one of the MCU's best third acts. But both Russo films also have to contend with poorly set up dynamics. I don't care about the Cap/Iron Man relationship until Civil War, nor Cap/Bucky until Winter Soldier, and the lack of set up does detract from what they do, despite overall I feel accomplishing it well.
So, that all being said, The Dark Knight Trilogy by a wide margin. I don't think we've had a superhero trilogy that has come close since, but I hope we will again soon.