There was an atricle in Guns and Ammo or some such magazine where Shotguns in the sandbox were discussed and the Pump came out favourite.
Perhaps for SWAT in the US Semi-auto is ok, but I won't trust my life to a risk.
For example, start with three breaching charges and five 00 buck. First three get you in the door and the remaining five are for assailants. Each has a different recoil profile. I won't risk that with a semi. Also in a military zone you can't always be sure of the ammo you are going to have on hand. Pumps don't care.
I've had the Benelli & the Beretta for about 20 years. I can change the barrel out on the Benelli to hunt birds with. As with all auto's you need to find what shell's that will feed & witch won't. The Benelli does not like lite bird loads other than that it's 100% so far. The Beretta will eat anything. NOTE: I'm a gun clean freak & they get cleaned after each shoot.
Although I think the Benelli is much sexyier (or most semi-autos for that reason) I had to vote for pump. In my experience (for what that is worth) they are more reliable. I consulted someone smarter than me that has used pumps in combat and they reported no memorable failures. My brothers infantry unit used them all the time, mostly for taking out door hinges. He said they were great and the bad guys feared them. I have heard that the new Benelli that the Marines got (M1014) has been reliable for them, at least from the little I have heard from end users.
I don't have a "home defense" shotgun but I will admit I want something sexy when I get one (why else would I get an XCR if I didn't like sexy) so I will probably end up with something in the Benelli line. I will always have my 870 in the safe, it is a good slug gun for dear.
As far as reliability goes, mine has been 100% in all respects since I've had it... I haven't ran many light loads through it, because it's role is that of a defensive shotgun-but for what it's worth those light loads ran just fine. More importantly, reduced recoil tactical stuff has ran perfectly-I guess the truly light stuff would just be a positive for less harsh training and cheaper practice.
I think the distinction between gas guns like the benelli m4 or rem 11-87/1100 and recoil op guns like my m2 are important too. I think the gas guns are more finicky/complicated and need more attention on upkeep than the recoil guns do.
Anyway, in my view, I'm more worried about short stroking a pump in the moment I need it most than a semi failing in some way.
I much prefer a pump I have had both, the semi auto that I carried in my police cruiser malfunctioned on me four time while I was doing my qualifications. It was cleaned by our armorer but I still did not trust it.My 870 police magnum pump has never failed me.