I would like to say hard choice but honestly, as much as I love them both Godfather p2 takes it without consideration.
I love the pace of it, it just flows well. The acting is pitch perfect from the cast and the art direction is great, very immersive with great colour, that works well with the grit of the story, giving everything class depsite how gruesome it is. I haven't watched it in years, I must of been 13 but it stuck with me as just a perfect gangster film. The kind today lacks in heavily.
Eternal Sunshine is fantastic and I wouldn't be surpirsed if other choose it over Godfather. Its story is original and more importantly believeable despite the concept being very far fetched. This is down to the great acting all round. Definatly, for me, the best romantic film ever made and I try my best to refrain from spewing hyberboles.
However, i love gangster moives (My favorite movie is Goodfellas) so one of those done brilliantly will (the majoity of the time) beat another genre done brilliantly.