Harry Potter, no contest.
Twilight's just a passing fad that all the 14 yr old girls will grow out of eventually. The Potter books/movies are great within themselves and have made their mark on society, cementing its legacy for a good long time.
And think about this:
If this latest Harry Potter movie wasn't pushed back to last week and instead was released at the November weekend it was supposed to....would Twilight even be as big as it is? Whether the two movies woulda been released in the same month, back-to-back weekends, or the SAME weekend, Twilight woulnd't have stood a chance. They got lucky as hell.