For me it is the MGS HD Collection. On the basis that you get so much for your money. MGS2 also has VR Missions, Alternate Missions and Snake Tales. MGS3 has 2 extra games, which are the original Metal Gear & Metal Gear 2. And Peace Walker is a great game, which also includes online mp and co-op with your friends. Combine this with trophy support, HD visuals running at 60fps, and you have a very good value for money product. It is worth the price for MGS3 alone, but an essential purchase for any MGS fan. Very high quality games that you will always come back to. :)
All depends on your prefernce, ICO is a lovely gem that isnt too heavily action oriented, and SOTC is absolutly brilliant.
MGS as much as i love them is sadly the game game with a different environment. I realised this after played Twin snakes > MGS2 > MGS3 the only difference where the visuals and the setting, same game all the way through tbh.