Worst Gun: Ruger Charger Pistol. I've upgraded every possible part of the gun and magazines, and that gun still can't make it through a 15 or 25 round magazine without a failure. This really surprised me because all of my other Ruger guns have been exceptional. Walther CCP M2 is a close second. It's horribly inaccurate and had to be sent back to Walther for reliability issues. At least the Walther was reliable when it came back from the factory (but I still can't shoot it worth a damn).
Worst Accessory: Licensed Ameriglo night sights for my Beretta APX Centurion. The first set snapped when my gunsmith attempted to install them. The tritium failed on the replacement they sent, which didn't even match the original sight. Some people want to blame this on the gunsmith, but he's been in town for decades, has an excellent reputation, and has done flawless work on several of my guns over the years. If only one type of sight gives him problems, I tend to believe the sight is poorly designed.
Best Gun: Pretty much everything else I own. As long as it goes bang when it's supposed to, and doesn't go bang when it's not supposed to, I'm a happy camper. A gun has to be pretty horrible for me not to like it.
Best Accessory: Sticky Holsters. I own many great accessories, but the Sticky Holster stands out because I was sure that it was just a gimmick. The holsters actually work, are incredibly comfortable, and are very affordable. They are my go-to holster for pocket or IWB carry when walking/jogging/running/working outside.