Ever since Quicksilver and the Scarlet Witch first joined up with Iron Man, Captain America, and Thor, way back in 1965, the bonds between the X-Men and the Avengers have been tight.
Oh, sure, they haven't always been on the best of terms, even going so far as to have an all-out war in 2012 during the Avengers vs. X-Men crossover, but usually you can find these two teams fighting side by side when the need arises.
It seems that whenever Earth's Mightiest Heroes need to bolster their ranks or have a complete reshuffle of the deck, they will, more than likely, turn to the mutant populace for help and fresh reinforcements. This has been done to varying degrees of success but the overall consensus seems to have been a positive one, with fans worldwide taking to these new additions of old favorites eagerly.
But which tenures have been the best? Not every X-Man to have joined the Avengers has made a good impression, but those who have went onto develop a synonymy with both teams.
Fans may complain about certain characters being oversaturated, but that doesn't detract from how good an alliance the one between the Avengers and X-Men has proven to be.