Terrific acting, that's for sure, but I think the first two Godfather flicks taken as a whole should get that honor.
The Godfather movies are great, no question -- although II is better than I in my opinion.
But Goodfellas hits harder because it is grittier, and doesn't romanticize the gangsters the way that GF films do.
Goodfellas shows what lowlives they are, whereas the GF makes them seem almost noble.
I find Goodfellas to be one of those movies that I always watch whenever I am channel surfing and run across it. I almost never watch the GF movies.