hmm...Well I liked Metal Gear Solid 2: Sons of Liberty than all the Metal Gears combined. It felt right at home for me since it was the first time me playing a Metal Gear game period.
So I choose MGS2: Sons of Liberty.
If MGS4 is anything like MGS2, then it seriously is a pick-up for me. Other than that MGS3 and MGS: Portable Ops on the PSP, put a sour taste in my mouth. I just couldn't find the urge to play those two games. I would either play Halo 3 or MotorStorm over those games and those games would collect dust. So I gave those away.