U.S. box art. The other two remind me of comic book illustrations, theough the european one isn't so bad.
I prefer the European art over the US because the US version looks like someone said, "Oh crap, let's take a random pic from the game and slap it on the cover'. I prefer covers that have a creative aspect to it, and I like the Euro over Jap version because it has more distinction.
I think people in this thread cant tell the difference between art, and CG screen shots of Snake's face. >_>
Kojima knows how to treat us Euopean's. All we need now are colour manuals. =D The EU one is the best. the Japanese one is a close second because it's similar, but the US one seems rushed and crap. I hope that one is a temp one.