I voted yes for the Semi-Auto. I had a barrel bushing break in a Colt combat commander that sent the bushing and recoil spring down range, another 1911 the firing pin retention plate slid out, and another that broke the slide stop. I've never had a catastrophic failure like that with anything but 1911s. That is why I won't carry one for defensive purposes.
I should have voted both though. I had a S&W 686 lock up once. I don't know why it did it but I was later able to get it open and it worked fine after that. I think it may have been a loose primer.
I have had a similar experience with a semi (not 1911) and also the revolver on many occasions (only because I have seen quite a few revolvers from different vendors shipping from the factory with bad "tolerances) with the the cylinder/frame measurements.
Point is IMO when you don't carry a BUG (even a little mouse-gun so small you forget it's there like a Bobcat, P-3AT etc.) you are always in potential danger if the primary gun malfunctions in any way (or you somehow loose control of it).
Anything man-made will at some point break (granted it's not something you read about everyday but I don't even want to chance it).