Well, it's not a movie, technically, but I prefer A Very Potter Sequel to A Very Potter Musical, even though I love them both.
It has Umbridge. And Lupin. And mentions of Gilderoy, and Dumbledore is called Big D, and there are centaurs, and...well, I loved the first too, and it was so hard to decide but I like the 2nd one just slightly better. THe same with the songs. Except for 'Gettin Back to Hogwarts' which is a classic!
Of course, sequels couldn't work without the originals though!
Same for books, I loved 'the Lollipop shoes' which followed 'Chocolat', but I wouldnt have without the first one.