I can't limit mine to one either...I like them all, but these 2 stand out above the rest:
First, my High-Standard Sentinel Deluxe .22
It belonged to my dad, and I have the original box and all of the original paperwork. I couldn't hit the broad side of a barn with it, but he could pop soda cans at 25 feet one handed all day long. I miss him.
Second would be my Star BM
It belonged to my brother, who, after showing it to me once, then cleaning it up and Duracoating it, gave it to me a couple of years ago at Christmas. He told me that it was his way of saying thank you for all I did for my parents while they were sick and everything I still do to help take care of our mom.
I've got several other handguns that I really like, but the stories behind these are what makes them so special to me.
Nobody can have just one favorite. Its inhuman to think a man can have only one favorite gun any more than he can have one favorite woman.
My S&W 29-2 has been the most accurate fast slick trouble free revolver I've ever owned. Mostly fired with .44 S&W Special handloads.
The Colt 1911A1 has been the fastest slickest most trouble free automatic I've ever owned. Its been retired for quite a few years now waiting its final disposition... to be sold for big bucks in order to feed some other need. I'll miss it.
The Colt Gov't was made in 1933 and was an Argentine Policia Federal pistol. Cheaply refinished by JLD and a bunch of new little springs and things installed by me, it shoots little groups at 25 yds and is as trouble free and slick and fast as the old 1911A1. When I lived in Indiana this was my concealed carry piece. I never felt undergunned.