Wow , that's kind of a tough choice for me as in reality some of the best movies i have seen are almost some of the worst - i love 'B' movies and made for tv movies. in fact i tend to choose movies by looking in the tv guide and if it has a 4 or 5 star review i generally give it a miss and if it only has 1 star i will probably watch it !
But if i had to make a choice from 'proper films' i guess the best would probably be out of Star wars original trilogy, die hard (all of them), batman begins, shawshank redemption or green mile maybe
Worst would possibly be Lotr (all of them), Star wars (the other 3), shaun of the dead and most of the Big films that the reviewers hype up as fantastic.