It really all depends on the Style of gameplay that you're going for. There are perks to all 3 types of airsoft guns out there.
Ill try to keep it simple and organized.
Spring rifles are fun if you're going for a certain type of role as an outdoor player. With a spring operated sniper, you're probably going to want to be playing much less aggressively than your other counterparts. Sping-powered Snipers are generally too big for cqb, too slow to re-chamber another round, and not ideal to be clearing multiple areas with.
Performance wise-
-they get consistant FPS
-they can travel far, fast, and accurate
-they dont require ANY battery scource. you can grab it and you're good to go.
-little maintinence
Now, lets talk about AEG's. even though they are battery operated, having a good quality/ reliable battery will ensure the performance and longevity of your gun. Aeg's can be good for feild or cqb gameplay, because you have large magazines, automatic fire, and maneuverability. its very easy to get from point A to point B, and clear whatever targets you need to. In a field scenario, when you see some enemies moving, you can easily hose them down and supress their fire, unlike having a spring-action sniper setup. you can also alter the fps, accuracy , and persormance of AEG's.
Performance wise-
-battery required to operate, but lasts a long time.
-upgradable in performance, longevity, and customizability
-easy to load magazines readily available with higher capacites
-maintinence required every once in a LONG while.
Now, lets talk gas guns. these types of weapons can be ideal for any type of gameplay that yu're looking to get into. but unlike AEG's, gas guns are powered by, you guessed it, gas. rather than a battery. Most people buy gas guns for the realism and satisfaction they are to shoot. but they can get hard to maintinence, and replacement parts are not always available. Another bad thing is that-the gas is stored in the magizenes, thus giving you LIMITED room for bb's. Every mag you own is suddenly a lowcap, and the gun needs it to even function! The #1 best perk about a gas gun though, is the trigger response. you gont have to wait on the gears of an AEG to cycle, because the second you pull that trigger, gas is released and your bb sent down range. These kinds of weapons are Ideal for CQB type enviornments, or even feilds. because that split second that one takes from firing off the first shot could mean life or death. (or staying in the game. lol)
Performance wise-
-realism
-trigger response
-generally high in fps, but downgradable for cqb.
-gas refill required to operate after EVERY magazine
Overall, and in my personal opinion, AEG's are the most Versitile weapons to own. Because you can alter them to perform any way you're looking to go with as an airsofter. You can make them shoot faster or harder. you can maintinence them, and EVERYTHING is easy to replace and readily available. You can install a barrel that will help you get better accuracy. you can upgrade your battery/wiring/gears to help you get a faster trigger response. And you can customize them to be ideal for any type of style that you want to play.
So AEG's would be the best choice.