The happiest contest in the world would be to try to name my favorite moment in the trilogy--no losers! But, among them:
--Vito and Bonasera at the wedding.
--Vito's face rising and falling when Hagen tells him about Sonny's murder, and when he uncovers Sonny at Bonasera's place.
--Vito's speech at the Don's Convention.
--Michael and Geary back and forth in the boathouse.
--Michael confronting Frankie in Frankie's office.
--Roth's soliloquey in Cuba.
--Michael's kiss of death to Fredo in Cuba, and the hug of death at Mama's wake.
...and about fifty others...