From what I've read, The Godfather was extremely romanticized. Meaning it cast a kinder light on the mob that was far from reality. Michael Franzese has done a couple of AMAs where he answers this question, and actually states the popularity of the film was a negative, because it made something as evil as the mafia desirable and something to strive for. He went on to state that Goodfellas was a much more realistic film.

Goodfellas is one of the more accurate movies on Italian-American organized crime. It's a fictionalized account of actual events like the Lufthansa Heist and the subsequent murders. It simplifies, streamlines, and omits elements of Hill's biography such as his stint in the army. The special edition of the dvd (and I presume the Bluray) has a very illuminating commentary from both Henry Hill and the FBI agent Edward McDonald. One of the more interesting gems from Hill is that the mobster Jimmy Conway was based off of used to party with the original cast of Saturday Night Live. he notes that this would probably have been too surreal for Scorsese to incorporate into the film.