I did a lot of research before buying a handgun. I'm an engineer, that's what we do. Talking with local police officers, I found many departments chose a GLOCK service pistol because of their reliability. Police Officers are notorious for taking poor care of their guns, but they count on them to function when they're draw.
What impressed me most about Glocks in general was hearing from officers who's departments chose a different serivce pistol, then went out and bought a Glock with their own money to carry on duty.
I bought the Glock 20 and set up a target at 20 yards. Anything within a 3" circle will hit the vitals on a person, and the Glock 20 will do that with ease.
While the recoil is strong, expecially with Full House (700+ ft-lbs at the muzzle) it's straight back into the grip thanks to the low lines of the Glock Action.
Since I bought the Model 20, I've pumped more than 3,000 rounds through it, American Eagle, Remington UMC, Corbon Golden Sabers and Double Tap 180gr 1250fps FMJs. It's eaten everything I've thrown at it and came up asking for more, even after shooting more than 500rd in a single session.
I picked up an after-market 6" hunting barrel and 22# recoil spring with tungstun guide rod. I was worried at first about the 22# spring with weaker factory ammunition and the stock barrel. I didn't need to be, even firing American Eagle 10mm (only 50fps more than their .40S&W load) and the stock barrel, the gun functions flawlessly with the 22# recoil spring, and the felt recoil is much lower with the heavier spring.
More recently I picked up an after market .40 S&W barrel for the Glock 20. The rounds are an odd fit in the magazine, and I've only run 100rds through this set-up, but even with the 22# recoil spring, no failure to fire, no failure to cycle.
The only down side? It's a Glock and it looks like a Glock - a Flat Black Box with a grip glued to the bottom. If you're looking for a flashy gun to show off in a velvet lined box and look pretty, don't buy a Glock, but if you're looking for a Power House that you can rely on to shoot the first time and EVERY time, the Glock 20 is the gun you are looking for.
22# recoil Spring (your wrist will thank you after a 500rd session at the rangs)
Captive Tungstun spring guide rod (add about 1.5Oz out front and makes swaping springs and barrels a snap.
Tritium Night-Sites - the High-Vis White on Black is good if there's any light available, but sometimes there isn't.
Brass Grip-Plug - Adds 2oz of weight, but really increases the moment of the gun and reduces muzzle flip.
The resulting gun weighs 33Oz plus ammunition but soaks up recoil like a feel steel-framed gun.
The positive lock-up of the barrel to slide fit and modular guide rod design makes break-down, clean up and barrel switching quick and simple (though I recommend a glove when swamping barrels at the range after pumping 250 rounds through a barrel)