I own a 20" bbl Mossberg 500. This loosely-fitted rattletrap has been flawless, though I've only fired probably 200 rounds through it (mostly 2 3/4" shells). I see no need to "move up" to a 590 for home defense. If I was buying a longer barreled shotgun for sport, I'd look harder at a Remington 870 Wingmaster, but to be honest I think a Moss 500 would be fine, too, and it would probably save me a couple hundred bucks.
1 vote for the 500.
edit: I didn't see the poll was closed! Well, I would have voted for the 500