Sal Polisi without a doubt.

Michael Franzese is at least intelligent and he doesn't act like he is/was some tough guy mafioso. He made a ton of money.

Dominick Montiglio was loosely connected with the infamous DeMeo crew and is basically the only one who has survived to tell the story. He does say a lot of BS but we're talking about the most overexposed rats not about the most lying rats. I don't think he's overexposed considering that he was close to Gaggi and supervised the DeMeo crew for him.

Joe Pistone has an interesting story and is an important figure in the history of LCN.

Sal Polisi on the other hand was a nobody and doesn't really have much to tell other that he 'knew' Gotti. That movie Sinatra Club seemed to be totally fictional.