I just rented out Rat Race - that is the best film ever!
Ahem, just kidding, but it is a shot at the worst film ever (along with Con Air...urgh...). It's impossible to say what the best film ever is. On individual scenes in films, I've always liked the bit in Jaws where Brody is throwing fish into the sea - the camera shot leaves a big empty space of water, with Brody on one side of the frame. You just know that something's going to fill that gap, and when Jaws does, Brody says, 'We need a bigger boat.'