The Avengers consist of a billionaire scientist, a Norse God and a Hulk who all, well, avenge—and all got their powers and skills a variety of different ways. But the X-Men are "mutants," who are just people born with extraordinary and powerful gifts. Living in a world that hates and fears them, the X-Men swear to make the world a better place by protecting both human and mutantkind—especially against forces of evil that stand in the way of human and mutant relations.
Unfortunately, X-Men's movie franchise is owned by 20th Century Fox while the Avengers are owned by Disney, so it'll be awhile before we get to see the teams face off in the movies. If ever.
In the comics, Quicksilver and Scarlet Witch were part of the X-Men, the Brotherhood of Evil Mutants, and the Avengers. So, both Marvel and Fox decided to feature Quicksilver in the movies.
Let's be honest: X-Men's movie franchise features a much better, faster and cooler Quicksilver. We won't spoil much, but "Age of Ultron" proved that universe's Quicksilver was the weakest link. And that's saying a lot since Hawkeye is typically the weakest Avenger.
But the "X-Men" variant of Quicksilver has not one, but two standout scenes. Quicksilver is better as an X-Men and definitely would kick some Avenger butt with the X-Men.
On one hand, Wolverine is a puny mutant compared to Hulk. But on the other hand, it's not like Wolverine can't out-smart the Hulk. Plus, Wolverine has a healing factor. (Umm, who are we kidding... Hulk would smash Wolverine to oblivion!)