Oh, and I just stuck on my Blu Ray of 'First Blood' in case anyone thought my last recommendation wasn't 'manly' enough... 
Deffo a toss-up between this masterpiece and the original 'Rocky' as to Stallone's best picture (Nighthawks might be a close third)...
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Much as it pains me to agree with Master Ray, yes, ROCKY and FIRST BLOOD are the greatest Sly films. More than that, they are simply great films.
What ruins the original ROCKY is II, III, IV, and V. Those sequels are just fun, stupid, overblown cartoons, while the original ROCKY is a fantastic example of classic 1970s gritty filmmaking. That film is raw. That film is real. A great character study about people on the outs in society. When you haven't seen it in a while and give it a go again, it is astonishing just how fine a film it is (and how fine an actor Stallone is).
FIRST BLOOD...uhh, nothing deep and meaningful (those scenes that attempt to be deep and meaningful are laughably bad), but as far as action goes...WOW. I'll use the words real and gritty again. Stallone's escape from the jail is one of the most thrilling experiences I've ever had in a movie theater.
As far as the third best Stallone film...Master Ray posits NIGHTHAWKS. Yes, a good film (Stallone made sequels to just about every piece of garbage he made, but this fine film no sequel. NIGHTHAWKS could have been a series of great Stallone/Billy Dee films), but NIGHTHAWKS is not Stallone's third best. That honor goes to PARADISE ALLEY. A sibling of ROCKY -- gutter people wanting a bit more out of life - the film is entertaining and touching. Great film. Little known, but still great.