Re: Help me chose a self/home defence gun
I think any variation of the Mossberg 500/590 platform is ideal. I use #4 buckshot as it still packs a wallop and rarely over-penetrates. In home defense (IMHO) a handgun should be the second line of firearms defense after the shotgun. Get some training on using a shotgun in close quarters. Nothing scares a baddie more than the sound of a 12 gauge being racked, except maybe for the sound of it being fired.
If you have your heart set on a handgun, consider if you are going to carry it or not. If you're not going to carry, then size and concealability is less of an issue. There are a number of good 9mm (and .40s and .45s) handguns under $500.