Well, I've owned several Semi's, including SKB, Browning, Remington, Mossberg, and now Benelli. None have ever jammed, failed to eject, or failed to feed. And they saw everything from dusty warm conditions in Oklahoma, to freezing wet conditions in North Dakota. If taken care of, they are pretty darned reliable.
I've also owned a couple of pumps. Mossberg and Winchester. The Winchester was a POS and I had numerous problems with it. Only a few cycling problems with the Mossy 500.
So, based on this 20+ years of experience with them, I'll take a well maintained Semi any day of the week over a pump.