1911. Like me it is simple and reliable. I know how to shoot it, take it apart and repair it if necessary. Ammo is relatively common for it. No plastic parts please - they don't age all that well over the decades a person might keep his "only" handgun.
Ruger sr40c. Great for cc, full size mag for range and stopping power for self defense and zombies. I wish they would make a .45 of the same size as the 40c and 9c, that would be perfect.
I gave this some thought after my last trip to the range. I have two handguns, a ruger mark III blued target 22lr and a glock 20SF 10mm. I love how powerful the 10mm is, but that 22lr is so much more accurate, and quicker to fire I'm going to say that right now if I had to take one pistol for everything I ever needed it'd be that ruger 22lr. The 20sf is a luxury item and if I could take it also that'd be great, but my first choice will be my ruger 22lr.
Anything that needs done inside of pistol shooting distances can be done with a 22lr.