I would favor GF1 slightly over GF2.

GF1 - I loved the way Michael calculated and strategized to take out his enemies in GF1. Taking care of all family business... the five families, Carlo, Moe Green etc..

GF2 - I loved the way he outsmarted Hyman Roth despite Fredo being a handicap for him. (Tom saying Roth played this one beautifully, I wanted to smack him) LOL

"What I want.... whats most important to me... is that I have a guarantee" - Train approaches.... Bang! Bang! Bang!