What pistol is the most ambiguous question in all of airsoft. there are so many variables and differences that it makes it almost impossible to narrow it down to a definitive answer.
First you need to decide what power platform you want.
Spring - weakest power output, single shot not advised for skirmishing
HFC134a (Tetrafluoroethane, or PC duster gas) - weak power, good reliability and resistant to temp changes.
Green Gas (or Propane) - good power capable of 300fps +, available nearly everywhere, performance is influenced by temperature. colder days lower fps, hotter days hotter fps. Green gas is the most inefficient in terms of consumption, you will / should refill the mag every other reload. Its expensive £10 for 300g of WE Premium green gas. Camping propane requires additional silicone to keep things lubricated. power will drop off as remaining gas volume reduces
C02 - Strongest power capable of 350+, easy to use, efficient some non blow back guns last up to 6 or 7 reloads on a single bulb.More consistent power than green gas, same lubrication issues with propane although C02 guns seem to be built a bit more robustly. Not as effected by temperature. Harder blowback. Some guns will shoot over power, the KWC desert eagle has been known to shoot 380fps out of the box. Its hard to adjust or regulate the power of a C02 gun.
Autamotic Electric Pistol or AEP - runs on a battery with a motor, reliable, consistent, cheap, weak and a bit boring, but great for playing in very cold environments.
Consider Blowback or Non Blowback. pretty obvious from the title blowback has a recoil, it moves the slide to replicate a real firearm and chambers the next bb. These are great for realism but use more gas. Non Blow Back are fixed slide, gas only propels the bb so there is less recoil and less wear damage.
Avoid full auto on a pistol. Its fun, but will leave you needing a back up, back up gun when you have no ammo left 2 seconds later.
Once you have decided on your power, you need to decide on what type of gun you like. You really need to hold them and feel them. They need to fit in your hand, they need to be comfortable and they need to be an extension of yourself to be effective as a pistol. For some people a glock is too small, for some people a glock is too top heavy, for some a glock is too big. In the real world, glock was designed as the utilitarian gun, good at everything, perfect at nothing and its popularity and success in the real world shows it. You really do need to get hands on and pick one that feels nice.
Things to remember are any moving parts will wear down eventually, so regular maintenance and lubrication of the internals is essential. It only takes a quick wipe and a strategic drop of silicon oil every so often.
Plastic slides and green gas are the most vulnerable to wear and tare, however upgrading a plastic slide gun to a metal slide gun is a headache and will never truly work as well as it should do. if you are concerned about wearing down a plastic slide then chose a metal slide. Having said that I ran almost 2000 rounds through my plastic slide with premium green gas and caused no visible damage at all, some claim (un verified) that green gas kills plastic slide maruis in just a few magazines.
Consider how many magazines you want and if they are available. I have a HFC185, brilliant gun almost identical to my TM at half the price and shoots just as accurately. But the magazines are now out of production, so obtaining a second would involve a costly import from Evike. WE and TM have generally good suppliers so you can be confident parts will be available.
And with magazine consider how many rounds you need. A dan westsern look the shizzle, but are overpowered and only 6 shots. A glock with a 50 round mag will terrify anyone but weighs a ton. a 1911 is a very nice gun, feel nice shoots nice, but most have 11 shots. Good for a backup, not good if you want to clear a building.
After all that it does come down to what you perceive your need of the pistol and then finding one that fits YOU. We can't tell you what gun will work for you, only you can decide.
TLDR: Buy my
Glock