I also prefer the TGS 2005 Snake and ill tell you why..
1... That white background really make snake stand out
2.. I like the darker utility belt more than the green or brown
3.. The gray hair keeps the characters look more fluent top to bottom
4.. That look... he seems to be looking right at me. The other pictures seem to be at a slight angle compare to the first. Plus his eye brows are slanted up a little more giving him the impression that he's scowling...

To me..... The TGS 05 Snake looks more like a bad ass....

both the first and last, but more the last because
its much more realistic and i liked the gray and brown colors, it goes well with his skin color, but his hair color would have been better if they made it like the first picture, so the only advantage the first pic has is the hair color, he looks not too old in it while in the last picture he looked so old, which is the closest to the reality, dont forget guys that a virus making him age so fast and is about to kill him, so its understandable if it makes all his hair white but yes the gray is better on him, he looks still have some strength in him with gray color! also i didnt like the greenish colors on his suit in the first picture because its so unreal!!

I kinda like the middle one. Fewer wrinkles so it makes him look somewhat younger. Makes him being on the battlefield a little bit more believeable.

where in the world this hairy pic come from lol!?

I believe that would be up Big Boss' alley. ;)

[Here's an excerpt from an EGM interview with Kojima concerning MGS4]

EGM: We were wondering if Snake's beard grew in real time and you had to shave it in a minigame?

HK: We actually first had that idea for MGS 2, but we weren't able to do real-time whisker shaving. So this time we also want to include that...hopefully we'll be able to get it in the final game. Also we'd like Snake's face to look older and to show realistic expressions of fatigue as he goes through the game. Well I told my team that, and they said, "Please, we don't want to have to do that." We're not sure what's going to happen with that.

Very intriguing :D

I'll take 2 over 4 also. And even without a number, I don't see how Code Veronica, my other favorite in the franchise, isn't mainline when it's the actual sequel to RE2.