If you want something reliable and affordable the Mossberg Maverick "security" edition is a great choice.
You can get it from Academy sports for under $200. It's built to swap MOST parts with the Mossberg 500 so if you want to swap grips or add a side saddle you can just get 500 parts.
I'll have to agree with this choice. Most home defense guns sit in the corner behind the door or under a bed and for me it's hard to have an expensive shotgun that you rarely shoot (typically) laying around collecting dust. If you plan on doing more with it then spend the money for a higher quality gun (tighter action, better finish, etc.) but since you said "home defense" then I'll assume it's going to sit.
With that being said I have a couple of 870's and have had Mossbergs and the Winchester Defender series. All great shotguns and would put my life on any of them to be honest.