If we are going to rank them in terms of awesomeness then this is the correct order:
Empire Strikes Back
Star Wars
Revenge of the Sith
Return of the Jedi
Attack of the Clones
Phantom Menace
If we are going to watch them in some particular order I think it goes:
4, 5, 6, 1, 2 and 3. I've been debating on what would be the best order to show it to the kids...