Just like in handguns....there are dozens of mfg's ...and literally dozens of models from each mfg ...on shotguns.../ its hard to pick a handgun for someone - and equally hard to pick a shotgun - especially if you're new to shotguns / what you want it for, etc.
But in general terms...a lot of us no longer depend on shotguns for defense...and shotguns that are typically setup for "tactical use only" ...tend to sit in the safe a long time and rarely get shot. Now that doesn't mean that a good pump shotgun is a bad investment. But the more versatile you can make the gun ...maybe the more you'll use it / and still have something you could use for Defense - but maybe not optimal as a "fighting shotgun"...something like a Browning BPS Hunter model with a 26" or 28" barrel - in my opinion, is a good long term pump shotgun...and a lot of gun for the money ...selling new at around $ 575 or so....
http://www.browning.com/products/cat...id=012&tid=211
A gun that has changeable screw in chokes - a barrel length of at least 26" ...and probably a 12ga these days is a very good general use shotgun. There are Mossberg, Remington, Benelli's and of course the Browning I put the link up for. The Browning is my favorite pump gun...but you may like one of the others better...depends on what fits you the best.
Before you buy ....I'd suggest you get with some buddies at the range and shoot a few different shotguns...find out what you like / what you don't like...and maybe what fits you / your eye is the rear sight on a shotgun - so how you mount the gun / how it fits you is critial to make the gun hit where you look.../ its very different than handguns - but similar to the concept of the grip angle on a handgun..