I've only seen the first and original "The Godfather". I haven't seen the sequels...
Welcome to the BB, Tru!
All three films deserve a viewing. (Actually, multiple viewings!) Of course, to ask which one is the
best film is really asking the unanswerable - like saying "How high is up?" or "Which came first - the chicken or the egg?"
Again, all three films have a lot of merit, and I think you will find them enjoyable.
And, let us not forget
The Godfather Saga (the television condensation of the first two films) and the other special versions available.
I think you're going to have many hours of worthwhile viewing.
Signor V.