That is easy...
This might surprise and upset some folks, but here it goes:
The biggest POS handgun that I've been exposed to was one that I chose not to buy after renting one. Hands down, the Smith and Wesson 617 .22lr. I was really disappointed when I rented one at the local range. I ran over 100 rounds of different types of .22 lr ammo through it before I was so disgusted that I stopped. The 617 "light-struck" at least 40% of the ammo that I tried that day. That same day, I tried a Ruger Mark II and shot from the same boxes of ammo and maybe had two or three ammo malfunctions, so I know the problem was not the ammo, but the 617. I had my heart set on getting a .22 lr revolver and really wanted the 617. I shot the Mark II, because I wanted to prove to myself that the ammo was the problem and not the 617. Seems to me that the springs were a little weak on that 617. I know that I could have bought the gun and changed the springs, but the experience left a bad taste in my mouth. I decided on a Ruger Single Six Hunter and have never looked back. I like the Hunter a lot. Looks great and is probably one of the most durable, reiable, and safe .22lr hadngun on the market. The Hunter is almost 46 ounces of SA stainless steel goodness!!