Good advise all around. My version:
1. Pump or auto? Pump. More reliable and just as fast with practice.
2 Finish? Parkerized. Cheaper and it defines "matte."
3. Pistol grip or rifle stock? Rifle stock. Pistol grips are harder to work with, specialized at best, and usually added as a gimick.
4. Sights or simple bead? Ghost ring sights. They are quick and if you ever need it allow for accuracy. Tritium front sight is a plus.
5. Mag size? It doesn't matter. One is all it takes. That said I like the extended magazines.
6. Gauge? 12. Though if it is too much for someone they move down to a 20.
7. Other accessories (light, side saddle, etc) I like side saddles for slugs. Lights can be an asset, though you must familiarize yourself with light tactics or they will be a liabilty. Lasers are for pointing at chalk boards and entertaining pets. Speed feed stocks are unnecessary.
8. Brand? Remington or Mossberg. Each has its fans. Each will serve you well.
9. Slugs? OO? Birdshot? Never birdshot. The rest depends on your situation.
http://www.firearmstactical.com/ has all the information you will need to make an informed decision.
10. Most impt HOW MUCH SHOULD I EXPECT TO PAY FOR ONE I WON'T EVER HAVE TO REPLACE? You will be hard pressed to wear out a shotgun. That said, there is no dollar amount that insures that you will not.
Hope this helps!
Erik