Saw a interview with Kevin Costner once where someone asked him about Waterworld and he said that it was a flawed movie and that almost all movies have some flaws. With that in mind I think the most flawless movie I've ever seen is Lawrence of Arabia. I just think that's as good as movie making gets.
In recent years I've been rethinking what exactly is a classic movie to me. I'll use a couple Mel Gibson movies as an example. Braveheart, a true classic in ever since of the word. I remember the fist time I watched it just setting for a few minutes after the movie ended and thinking wow, what a great film. Now I've watched that film from beginning to end maybe three times? Another Gibson film I like is called Payback. Not exactly a block buster but I bet I've seen that movie at least a dozen times. Its just one of those movies and never get tired of and can watch over and over again. So which film is really the classic?