I don't know about "worst" but if you mean "least liked", mine was a SA 1911. I bought it used about 9 years ago. Here is a list of the problems and issues I had:
- Would not chamber the last round of either mag that came with it (not sure they were the factory mags though)
- Rear sight slid out of the dovetail after 50 rounds - fixed with loc-tite
- Sights were good but were totally black so I couldn't see them in the dark
- 2-piece full-length guide rod kept coming apart
- Had an interesting "double feed" issue - fixed that with Wilson mags
- Was made in Brazil - not necessarily a "bad" thing but I bought it thinking it was American made
- Extractor had the clocking issue
- Slide was not milled properly (the radius on the top was assymetrical) - didn't affect the performance but was annoying to look at
- Cocking serrations were so sharp they almost drew blood.
- Was the old grip configuration (different front strap shape) and had a smooth front strap so I had trouble hanging on to it
Overall the gun wasn't so much "bad" as it was a disappointment. What really gets me is there was a brand new one right beside it in the case and I passed on it for this one to save a little money (less than $100.00).
Many of these could have been fixed by SA but I was never happy with it so I sold it at a loss. I called them but they said they would only honor the warranty for the original owner - guess I should have phrased the question differently but in the end the best thing for me and it was for us to part company.
I still want a 1911 but I think I'll go another way next time - perhaps a Kimber or Colt, though I don't by any means think SA makes a bad gun and I might try them again.
I also had a Ruger Single Six 22LR/22WMR that I did not like. It wasn't a bad gun either but my fingers are too fat to load it. The cases tended to stick in the chambers after firing but I fixed that with a bath in transmission fluid. It was stolen.
EDIT - the Single Six was stolen FROM me, not BY me