Michael, he was smart and calm, but irritated me with his stone cold heart. The way he started treating Tom towards the end of Godfather 2, that kind of heartlessness.
I liked Tony a lot, he had balls, a godly sense of humour and was also had a heart, though the coke and power fucked him up.

Realistically Michael would easily live longer than Tony. But in terms of who I'm more fond of it gotta be Tony.