You can't go wrong with a Mossberg 500 or Remington 870 (with traditional stock), although many favor the safety location of the Mossberg. However, if you're using the pistol grip/shoulder stock type stock some have posted here, the Rem 870 might be better for you. Still, either are extremely reliable and proven by time and service by various military and law enforcement all over the world.
Semi autos of today are reliable, but if for whatever reason you do not hold them correctly, or something else weird happens where it doesn't recoil properly, it might not work the action properly. A pump will never jam for that reason - generally it jams if you short stroke, or something else - user error. That obviously wouldn't happen in a semi auto. So there's a quick look at both platforms in general, but the short stroke issue disappears with some experience. It's not a real issue.