GOTG all the way. Nothing else is even close.
Never been a fan of Captain America, and while the action is impressive in TWS, I think a lot of people confuse action with acting - as I still find Chris Evans pretty two-dimensional (although that was an improvement from Cap 1, in which he was one-dimensional). The fight scenes were great, but I struggled to really give a **** about Cap and his moral dillemmas, or about any of the other characters - especially Bucky, who did plenty of glaring, kicking and punching, but not a lot of acting.
Strangely, I cared a lot more about a walking tree and a talking raccoon, who were a lot more interesting and fun. But that's just me.
In fact, DOFP, while a great watch, hasn't struck me as particularly memorable. Fassbender, Macavoy and Jackman were all great, but for some reason the film still felt kind of hollow - unlike the source material, which is some of the best Xmen stories ever.
Yeah, despite the fact that they've not had a single movie to establish the characters, and not one of them is really particularly iconic or part of the public consciousness, ( I sort of think of them as Marvel's B-list characters), still they managed to be a lot of more enjoyable to watch than either Cap or the X-men or Spider Man.
To be fair, GOTG was a slightly different genre, as it was a lot closer to Star Wars than the Avengers - so not really a superhero film, but still a comic book movie. Despite the fact that the tone was reasonably light, the villains were still a credible threat, and there were plenty of good character moments ( a lot more than in the Avengers ).
Having said all that, GOTG was more fun than I've had at the movies in ages - and being a pretty staunch DC fan, I can say that GOTG was the best CBM since the Dark Knight. But this is all IMO, so if others see thing differently, fair enough.