Both are very good, but i thought De Niro outshone Al Pacino in The Godfather 2. And Deniro plays more complexed characters than Al Pacino does. Another thing is DeNiro has the New York Italian American cool to him that Al Pacino does not have. Plus, the Deniro- Scorsese partership was one of the best director actor partnership. Al Pacino has better films to his credit because of his work with a good director. Films like mean streets, casino, goodfellas, taxi driver are among the best movies ever made. And who can forget the Russian roulette scene with Christopher Walken in Deer Hunter. Check out my videos to see a Robert deniro scene from taxi driver. I will try to upload a scene of Deer hunter as well.
They are both amazing actors, who have put on some of the greatest and most memorable performances of all time. But of the two I much prefer Al Pacino. I do however have a bias towards him because many of his performances and movies are the reason I became such a huge film buff, and I've seen so much of his work. He has just always had this rage within him and range that made him mesmerizing and fun to watch no matter what character he is playing. Whether it is a coked up psychotic drug lord in Scarface or tired and beaten down failed writter in Chinese Coffee, you could never take your eyes off of him. After watching some documentaries about him and reading a book of interviews he did, I have come to admire him even more, the way he approaches his roles and the love he has for acting, whether it be in front of the camera or on stage. Pacino is definitely my favorite actor of all time.