Another vote for the sxs but designed thusly:
20" barrels, rifle sights, half pistol grip (formally known in the trade as a Prince of Wales grip, informally and coarsely known as the limp d**k grip).
The right barrel would be choked Light Modified. The left barrel would be rifled. The gun would have twin triggers and I could instantly buckshot or a slug. The ammo would be Federal Tactical 00 or 000Buck and Federal Tactical Slugs so I could get the gun with 2-3/4" chambers.
It would be a true sidelock ensuring that should a spring or firing pin break I would have full use of the other barrel. The lock would be made with coil springs which are more reliable. It would be a self-opener for those rapid reloads.
Weight would be around 7lbs and I would have a second barrel, 29 inches choked IC and Mod for upland game hunting. The longer barrels would struck thinner and weigh the same as the shorter tubes to ensure consistent balance.
The gun would come with a custom stock of fancy Turkish walnut with a very slim Silver's recoil pad. It would come in a French-fitted case with all of the accessories including a monogramed, Kevlar-lined, bathrobe with shell loops and a slight recoil pad on the shoulder. Just the ticket for those late night intrusions.
For the truly well-heeled home defender, a matched pair might be in order. You could give one to your wife or, more appropriately, train her to be your loader.
This is not entirely a flight of fancy. Ugartechea in Spain makes a short barrelled rifle-sighted sxs gun for boar hunters. I'm sure they could make a similar barrel set for one of their higher grade sidelocks.
Now, all I have to do is win the lottery.
Paul