Why stainless? My Browning Auto5 and Remington work fine and the Browning is mechanical rather than gas so it really doesn't have a lot of issues, even when wet.
Get any good pump gun with an 18" barrel... Remington 870 , Mossberg 500 . Why a pump ? Because everyone knows that sound of you racking in the first round. Ammo... opinions differ, but I like #4 buck for the first 2 then finish with slugs.
Remington 870 Tactical is tough to beat for the price. I bought mine at Bass Pro for $340 after tax at the end of summer. They price matched my local Wal-Mart.
This round is great! 3 pellets of 00 plated buckshot WITH a slug.
Personally I like the semi-auto's better, especially for quick follow-ups. I don't like to rack any gun as a warning to the intruder, a verbal warning and a quick blip of light is all he needs to hear & see. The semi-auto's are typically more expensive though.
The Benelli M4 is a bada$$ semi-auto shotgun! Not in my price range at the moment, but I will own one. Lots of accessories are available for it, and you can easily add an extension tube for a couple extra rounds.
the ultimate in conflict resolution.... to hell with the auto part(not even that fast) its all about the "recoil system" so you can stay accurate for more than one shot
Why put a lot of $$ in something the cops will end up with? You can BET yurass, they will take it with them, if you ever have to use it.
Our local "fuzz" recommend #6 shot. That's what I have in my Maverick 88. Gives good coverage at 50'.
Why warn the perp?? He may already be set on kill. If he's already in the house, it's time to TCOB.
For that reason, my 88 has a full load and 1 in the chamber...A true "point and clik" device!