Me and my mates have all been getting into airsoft lately, and there is a heck of a lot to choose from. Phantom linked you to a gun thread but its in a members-only section of the forum, so you probably won't be able to view that if you aren't a member. I'll repost it here for you (these are Phantoms remember)
As somebody who has just gone through this process, there really is a ton of information to take into account. First there is your playstyle, then your preferred location, then preferred weight, then looks and camo and accessories and then (and this is the big one) your budget.
2 of my friends bought pretty standard M4's, and while they are the cheapest guns in the group the are also the most boring. They are starting to get sick of all having essentially the same gun. And while there is so so much that can be done to it, at the end of the day its still and M4.
After much deliberation, I bought the ARES Scar H. It was my favorite gun from what was available, was a good size, really awesome weight and had so much metal in it. But there is a list of problems that go with it. Mine was chosen more for looks than functionality, and while it is pretty accurate atm it still needs a lot to be done internally to become a proper weapon. It is also so heavy that before I got my sling my forearms would cramp after 3-4 hours of playing with it. But I love it, and as far as I'm considered it is the best looking and most realistic gun of my mates by a mile.
Its also the one that has had to be fixed the most. Oh, and at $800 it was the most expensive, costing more than twice the price of some of my friends guns.
Another friend bought the L86, and he really likes it. Its pretty reliable, looks great and is very functional. It means he has taken up a suppression role in games, which he enjoys, while the rest of us do all the running and jumping. But again, it was a bit more expensive than alternatives.
Another went for the cheap, buying the JG G3 SAS. It was actually a pretty decent buy and has been running really well since he got it. Could have gotten 3 for the price of my Scar. But he pays for it in other areas. It feels extremely fake, has no weight to it, isn't as accurate as ours, and just detracts from the whole realism of his game. He hardly uses it any more, instead using his VSR-10 and a Glock.
Me and a friend got the SRC H&K 416. It really is the best of the M4 style weapons. There is a lot different to it and it shows. It looks and feels much better than the other M4 variants, but is a bit pricier. But chuck a holographic on it and you are away with a really light, versatile weapon.
So. Just think everything through. For me the Scar H always seemed to stand out. Go into ASGC, have a look around and see if anything pops out at you. You should be getting a gun that makes you smile every time you look at it, not one that makes you regret not getting that other one. If you have a favourite gun from MW2, try that. If you watch Stargate, get a P90, MP5 or G36. Its all about getting the right balance with a ton of different factors. Good luck