The Godfather, Part One, has some substance. Character development, plot, excellent direction and acting - a film with some depth - no matter the message.
I enjoyed both. Scarface is a bit of a joke. Pacino's usual overacting, lots of blood, explosions, bad accents, mindless junk. Fun if you don't feel like thinking and just want a well made, shoot-em up comic book.
The Godfather is decent cinema. Not exactly Citizen Kane, but better than average film.
Both have a place, but I don't really think they are comparable. To beat the cliché to death - apples and oranges. Similar on a superficial level - crime dramas. But one is a serious film, the other over the top, well made, junk.
I'd take The Godfather over Scarface anyday. Scarface is still good, but it's nowhere near the level of The Godfather. Now if I had to pick between Scarface and The Godfather 3 it would be Scarface hands down.