I think the accent of Tony in Scarface was a bit overdone; sort of a characature rather than authentic ( I've heard many Cubans speak English.). Tony was like tough Ricky Ricardo of 'I Love Lucy' fame. Desi Arnaz deliberately went over the top with his accent.

I did very much admire his capture of a New York Harlem Puerto Rican accent in 'Carlito's Way'.
He did his best work though, to me, in 'Brasco' for his portrayal of the non-glamorous position of the small-time made worker in the mob. I could smell the street in his character in 'Brasco'.