Well, frankly (to the op) you've chosen 3 shotguns that are pretty dissimilar to each other.
The 870 is basically the 'classic' tactical shotgun, if that's what you're looking for. Best aftermarket support, simple to use, as reliable as most pump actions tend to be.
The 887 has a 3.5" super magnum chamber, although I'm not sure exactly what you'd use that for. It also has a really infamously bad reputation, so I'd probably go with the 870 over the 887.
The 930 is really the oddball out of your 3 picks, being an autoloader. There's no doubt in my mind that for defensive purposes, and you have the choice between the two, there's no real reason to go for a pump over an auto. Autos might be more 'ammo picky' but you're going to test it and choose rounds that function reliably anyway, aren't you? The other thing though, is that last I checked the 930 costs almost twice as much as the 870. The question is, is it worth the extra 2-300 bucks to you? I can't answer that one for you.
So, bottom line, I'd avoid the 887 (if you really want a 3.5" super mag chamber, I'll second the Benelli Supernova), and between the 870 and the 930, you decide if you want the more expensive autoloader, or the less expensive pump action.
