I think the X-Men as characters and a group dynamic are cooler than The Avengers ...buuuut, Ironman and The Hulk are awesome and it was great to have them in the same movie.
The first two X-Men movies still hold up. Ian McKellen as Magneto & Patrick Stewart as Prof. X was genius casting. Avengers wins on pure spectacle ...but I think I still like X-Men 1 & 2 better overall.