It's fiction, right? Why not go with something interesting - something atypical? Or, do you want your main character to be use the "tool" that his superiors told him to use or gave to him?
Here are some suggestions:
HK P7M13 with suppressor
Smith Wesson Model 327PC Scandium 8-Shot 357 Mag - maybe your character is a revolver guy who wants to make sure he doesn't leave any casings behind
Custom STI 2011 double-stack .45
Sig X-Five -
Glock 29 - 10mm
What's the point of making one of your characters some kind of secret squirrel if he's going to carry a standard 1911, Beretta 92, Glock 17, etc?
I have a better one. He uses Patton's Single Action Army, he swiped the real one and substituted a replica.
Make your character memorable. Give him the handgun equivalent of Anduril or Sting or Mjolnir.