I am a big fan of both. Al Pacino has it hands down though IMO. Films like "You don't know jack" (recent) really show off his versatility. Also in "Scent of a woman" you do see alot of Al's trademark characteristics, however at the same time he's doing an extraordinary job of portraying a blind war vet. To this day, Carlito's way continues to be my favorite movie. Outstanding performances from both Al Pacino and Sean Penn make this movie an instant classic. Don't get me wrong, I love Robert Deniro and can name just as many titles where he has seriously owned the screen and his role. But when it comes down to the two and im forced to make a choice, it is going to be Al everytime.