I would have to say Godfather 1 and 2 are the best for me. It has so many epic moments. Goodfellas is really great too though.

I extract my inspiration from the Godfather. Unfortunately Scarface is a little too modern for a 1920's theme.

Godfather II is a good movie :)

I will go with Goodfellas.

I love Casino, 

I don't think you can beat timeless classics like GF or Goodfellows

Nothing will ever beat Godfather.. Except Godfather 2

A Bronx tale is very good and should be up there as well. I think it's underrated but it's a learning movie about real life things and about mobsters both and it doesn't exactly glorify them either 

I loved the Godfather one and two.  Then there was all of James Cagney movies.  

has to be the godfather part 1

The series of GodFather's was good one

There are some real classics that could be mentioned here... As mentioned in the early posts, Reservoir Dogs is an amazing film and is made really well - not like your average movie which makes it that much better. However, if I was stuck and had to choose only one mafia film to watch for the rest of my life, it'd have to be Goodfellas.

As most have said, the Godfather series is an obvious choice but honestly, only the first one was a GREAT, in my opinion. The other two were good, don't get me wrong, but I could watch Goodfellas over and over without getting sick of it - in fact, I have.

Shoutout for 'Donnie Brasco' - maybe not the best, but well worth a little mention!

I think Scarface should still be considered a mafia movie, it's a gangster movie but still similar.

Hands down the GodFather series.