I go Airsoft pretty regulary and it's a great hobby. As for the weapons it's more about what you like, sure there're alot of differences in quality, weight etc. I've personally used P90, AK47 and AUG and I'd recommend any of them. If you'd like to be a sniper then be ready to get a good sidearm as well since most games have limit on how short range you can use the Sniper (they're too powerful for shooting at short range).
Also if you want something in between then I liked my configuration of AUG with an silencer and PSG-1 accuracy barrel. Since AUG is a bullpup the PSG-1 barrel fits in with a silencer (it fills about half of the silencer but the silencing effect is still noticeable). With M120 mods (muzzle velocity 120m/s) it worked great as a sniper too. Modded M203 to it for additional close combat power, 165bbs on a short range is devastating :P Also I loved the AUGs triggering mechanims, pull the trigger halfway and it shoots one, pull it all the way and you have full auto, great for panic shooting
As for other equipment camosuit and tactical vest are pretty much mandatory. Without tactical vest you're fucked when you need to change a clip. Radio also makes it much more enjoyable since you can coordinate with your friends

Of course if you're tight on budget you can start with just the weapon, glasses and camo suit (camo is really mandatory, otherwise you're pretty much saying SHOOT ME).
Currently my equipment set is:
Main weapon is P90, M120 mods, silencer, longer accuracy barrel, surefire tactical light, selfmade quick lock sling (move the weapon to my back and it sticks there).
Sidearm MK23, laser sight, tactical light, silencer.
Radio.
Tactical vest with leg holster for pistol and extra pouches on another leg.
Black, Snow & Camo suit.
Self made smoke grenades and "flashbangs" (just a small flash, rest if roleplaying).
The best (and most expensive) night vision goggles.
I've probably spent around 2000e for the equipment and probably 500e or so for bbs and gas. Airsofting isn't the cheapest hobby but it's so damn enjoyable that you'll be happy to spend loads of money for it.
If you have a weapon you'd like I can give comments on most of them

Generally the only difference is weight, accuracy and sturdiness. Alot of weapons have plastic creak. Accuracy is directly related to the lenght of the barrel. Standard velocity on AEGs is around 90m/s (M90). And of course how it looks which is usually the deciding factor for a weapon :P