Originally Posted by Kurtz

You don't need to wory about over penatration with anything short of a high powered rifle (think 30-06 and up).

You have to get training. If you keep a gun for home defense and don't get training on how to use it you will be endangering your friends and family. No exceptions.

As far as the gun, the winchester 1300, remington 870, and mossberg 500s are all going to be basicaly identical to a new user. Some features you will want:
1) A magizine tube that extends to the muzzle
2) A barrel no shorter than 16 inches and no longer than 20
3) A fiber optic or tritium front site (a brass bead will be invisable in the dark)

Again, If you don't know how to use and safly store your gun, you'll end up makeing yourself less safe.