I will unashamedly stand up and count Watchmen as my favorite, followed closely by The Avengers, V for Vendetta, Dick Tracy, Iron Man, Batman Begins and The Dark Knight.
Worst? Jeez. Pretty much any "superhero" film before 1998 that didn't feature Batman or Superman, but including Superman III, Superman IV and Batman & Robin. After that, there's Catwoman, Elektra, both Fantastic Four movies, among others. But my all-time least favorite: League of Extraordinary Gentlemen, the only movie of any genre that has ever caused me to fall asleep in the theater. What a TERRIBLE way for Sean Connery's (live-action) film career to end!