What is it with all you Nancies and this .. Why do you need it for self defense, call the police, blah blah blah...grow a pair you wankers. If the guy wants advice on a Semi for protection, give advice on the question, don't prove your a B!tch by getting him to justify why he want's it. Do you justify why you want to own a firearm...no I didn't think so. If you have nothing constructive to add, move on to the EE section on buying some testicals.
Now back to the original question, if your looking for rock solid reliability in a defensive semi auto shotgun, I think the Benelli M4 is the way to go. Proven reliability, mag a capacity, 8 rounds with Ghost loading. There's a reason the US military use them, because they go bang every time, and that's what you want. It's pricey, but it comes down to you get what you pay for.