Probably my favorite Sly movie after all these years is still Nighthawks. He gives a serious and intense performance and is nicely paired with Billy Dee Williams. It helped having Rutger Hauer as the villain, at the time still lean, mean and dangerous. Great location work as well in New York City (interesting trivia - this was originally meant to be French Connection III, but Gene Hackman turned down a third go-round as Popeye Doyle).

F.I.S.T is a fair movie that could have been great, except I find Stallone pretty stiff in it. I like him in Tango & Cash where he gives one of his most relaxed performances (though the movie itself is too chaotic).