.410 would be sweet. Always have been drawn to a .410 double. Would work way better than a 10 ga. and better than a 12 ga. even. A 20 ga. would be ideal. A .410 looks like a .410 where a 20 would look bigger to the intruder and still be manageable. Think about shooting a 10 ga. then think about shooting a short one. Does not good to blow a hole in the cieling and end up with the gun behind you. If you hang on to it, recovery would be slow. Scare factor definately should not be counted on, should only be used in your favor. If you scare the BG away, GOOD. If not then you most definately have a situation on your hands. You can only count on controlability and accuracy. Shoot some paper plates froom 10 feet away and 5 feet. Look at the patern size. Really doesn't matter if you use #12 bird shot or slugs. You will still need the same accuraccy. The choice between shot, buck shot, or slugs, is penatration. Who will be on the other side of the wall. We can't help ourselves, we think of a shotgun as a street sweeper, or an alley cleaner, but it's not. At ten feet you need the same accuracy as with a rifle or pistol. The advantage of a shotgun is less penetration, if you use shot, not the patern. A double can be made shorter than a pump ( making it handier in the house), a short double has a good scare factor that might work in your favor (maybe) but, think of sneaking through somebody elses house and hearing the rack-rack of a pump. Definately would rattle my nerves.
I think the problem with this subject is that so many ideas have good points, but you cannot put them all together in one gun. Take your 26" pump gun, for instance. Afterwords the officer investigating is going to see "bird" gun, That you defended yourself and family with. Not some sawed off, decked out "man killer". He is going to be more simpathetic to you. If you live through it.