casino = great
goodfellas = classic
goodfellas wasn't as fabricated as casino seemed to be. i researched both stories and the stuff in goodfellas lines up alot better than it did in casino.
But imo that doesn't have to make it a lesser movie.
For instance, a movie like Lawrence of Arabia which is meant to be a biography, is also fabricated for a large part. However, it is still considered one of the greatest films of all time.
People tend to forget that the main purpose of a film is 'entertaining'. If you want to know all the facts, you should read a book.