Marlon Brando and Robert De Niro play the same role in the godfather trilogy? Which is better and why?

It's the same role. Marlon Brando plays Vito Corleone from middle age to old age, and De Niro plays Vito Corleone as a young one.

As for who performed well, I'm afraid it's a matter of opinion.

Brando born in 1924 is older than De Niro born in 1943 19 years old. The director's casting is very suitable, they just represent two stages. The performance styles of the two people are also different. De Niro is young, so he plays the godfather full of tension, explosiveness and disillusionment. Brando is an experienced godfather, full of charm, strong sense of hierarchy and sophisticated. I like them both very much.

The beauty of the godfather is the courage and wisdom of the special men of the protagonists. You will find that they are not called mafia or gangs themselves, but "families". All people do their best for their families, which is all the qualities that men should have. So don't worry about who performs better, because movies are classics.