I voted for GF I.
Nothing compares to it. GF II is also one of the best movies ever and the flashback scenes are the best but no way the rest of the movie comes any closer to the first.
Gf II is a lot about business and about the SEPARATION of a family - Michael from his brother / Michael from his wife etc.

Marlon Brando IS the Godfather, its about being a strong family, united - the first scenes after Vito gets shot when they all join forces together to decide what to do - THATS THE FEELING OF A FAMILY WE ALL LIKE TO WATCH!

Marlon Brando sitting in the garden with his son Michael -
"I never wanted this for you..../ we'll get there pa....
This is how you feel the family and how you connect to the family, this is why The Godfather I is the best movie, because of the "Family Feeling".

Why is it that Godfather II's best scene is actually the one with Caan - the last flashback scene? because once again, its the feeling of the family which Caan is giving us so perfectly...

As for GF III - its a good movie. But it couldve been much better. Funny...They waited 16 years for a sequel, yet this is the only movie that looks as if its been made in a rush. But still, its a good Godfather.

One is THE BEST
1 is better than 2 but 1+2 are all together better than 3
and i think if they do a 4 i think they should return to the elements that made 1 a "classic"