Pistols in airsoft typically function as a backup weapon in airsoft games, or for those who play mostly close quarters or like the challenge, they may even serve as a primary weapon. Pistols are often easy to get into due to their lower price compared to rifles. Within the pistol category there are several different types of pistols in terms of operation and level of realism. The one that works best for you will have to be based on your budget, how you plan to use this pistol, and how much realism you want. Let's talk about the types of pistols first based on the least expensive types of pistols and move our way up.
Gas Blowbacks - Full Blowback Gas Powered
The top tier of pistols would be the gas blowbacks. These can be powered by CO2 or green gas which will be stored in the magazine. CO2 pistols will perform better year around, especially if you live in an area that sees cold weather. Green gas works better in the warmer climates. The advantage to green gas is that the magazines serve as gas tanks which you can always top off between rounds so you're not questioning if your gun has gas in it or not. For CO2 you need to get to know your gun to know when you should replace the cartridge. Often times the CO2 capsules last about ~2 magazines for most guns. The downside to green gas though is poor performance in cold areas. These pistols will feature full blowback and function and cycle like the real thing. You can also field strip these pistols down for cleaning and maintenance as you would on the real thing.
Let's go into more detail about the advantages for a second. In CO2 pistols, you're often not using the full capsule when you are playing. How much you get out of the capsule before replacing it depends on the gun type. Blowback pistols will often be able to shoot 2 magazines worth on a fresh CO2 capsule. Knowing this, there's often enough CO2 for a few more shots. But you don't want to be on the field facing down another player when your CO2 pistol is suddenly empty. Back to gas guns, since the magazine is basically a gas tank you can always fill it to the top and never have to second guess whether you are loaded with gas or not. Some say it is actually cheaper than CO2 in some cases, though we leave that up for debate. Green gas is better left to warmer climates so you should consider where you plan to use a green gas pistol,
Now let's talk about disassembly and why that might be an important feature. For those that plan in a relatively clean environment (like an indoor CQB arena), any type of pistol can work well for you. If you play outdoors where it can be dirty or muddy, being able to fully disassemble your pistol will be a huge plus. Being able to do this means you can deep clean your pistol so that it may last longer and shoot better. Airsoft pistols that can be broken down and disassembled like the real thing can be kept in better shape and running longer.