To give a bit of an alternate viewpoint...
Where you are going to play and how you play really effects what you should start with. If you are a shoot first, ask questions later, KILL EVERYTHING type of player, you are going to want a AEG. Gas rifles are fun to be sure but have several major downsides. They have a much higher startup cost, need relatively expensive parts to use at low FPS events/fields, and are harder to find replacement parts for.
Gas pistols are fun, a bit cheaper than gas rifles, and generally more reliable. I primarily only run with my KWA USPc when playing CQB. However it's pretty limited from a range standpoint so you will be hard pressed to remain competitive at an outdoors game.
AEG's are relatively cheap, quite reliable (if you don't futz with them), and you can find most the parts you want/need locally. Just stick with a common platform (M4/AK) for your first gun. Yes, everyone has one, but that means everyone also had parts.
The other thing worth considering is an AEP. The clones are VERY cheap, VERY quiet, and very reliable (once again, if you don't futz with it). Upgrade/replacement parts ARE nearly non-existent, however it's not a huge issue for AEP's. Replace the stock NiCd/NiMh battery with a small LiPo and it's ready to go. They might be the least intimidating sounding airsoft gun you will ever handle and may even get some laughs from other players. That usually ends once you get on the field. For those of you who have faced my MP7 on the field, you know what I'm talking about. You can't hear it from 5 feet away, and it's got more range plus better accuracy than 99% of gas pistols.
