Idk who oem's that socom gear gun but on that list i would stick to the G&G, G&P or the classic army. Another good brand not represented on your list is VFC. IMO none of those would necessarily be a bad choice as long as they don't have a blowback system. Just make sure you get one with a metal receiver.
There's no "best gun" in that list so it very much boils down to personal preference. Most people would probably say G&P is the better manufacturer, but the other two aren't bad either. The guns listed have a variety of barrel lengths, thats something to consider when choosing between them i.e. where will you be playing and how will you be using it.
All of them have "marui compatible" internals which are decent out of the box so IMO consider externals. A lot of people go for the M4 A1 and chose to customize it themselves. Nothing wrong with that route but is can get pricey if you are replacing a bunch externals e.g. rail systems. Try to get something as close to what you want externally it will save you some dough if you chose to customize it in future.
Last edited by Kozzie; October 3rd, 2013 at 13:52..