I think most older people will remember him as Michael Corleone, but the younger generation that is more into violence and drugs are more likely to remember him as Tony Montana. Whats funny is noone will remember him as Lieutenant Colonel Frank Slade, which is still the only role he won an oscar for.
However, despite considering myself as being in the younger generation, I will remember him as Michael Corleone because that was the first time I became a huge fan of him and realized how great of an actor he really is.