"Tactical" is essentially derived from "use in battle" or the ability to do so. It's basically the battle (or your adversary) that decides whether or not a weapon is tactical. In truth you could interchange "practical" and "tactical" it would have the same effect basically.
I'd say every scenario warrants thinking it through for each individual. I would not go into combat with one (not willingly anyway) or put myself into a situation where there are multiple targets in close quarters. But, if I found myself there I think that I could manage. I also would not choose an AR for HD either.
If I had to choose one for the sole purpose of HD it would be one of the 1894 variants or the 1892 Win Trapper because of the calibers and the smaller barrels. Both come in large pistol calibers and have a mag cap of 9-10 with 16" (ish) barrels.
What features would you have on it or do you think it SHOULD have?
Enough ammo to do the job, a way to aim it, and most importantly, proficiency in making the weapon serve it's intended purpose. Most home invasions happen at night so being able to quickly acquire a target at night is essential. Otherwise I (meaning me personally) wouldn't gadgetize a HD weapon.
I am sort of an advocate of laser sights for HD, and here's why; hopefully none of us will ever have to go thru this, but... When it all happens the fight or flight switch is going to kick in and it results in adrenaline. There's an intimidation factor as well. There's also an "I gave my position away" factor too, but I think that it's still worth it in the end. My girlfriend and I will both grab our pistols, I keep mine until I clear my sons room and then I using the street howitzer. I'd go with night sights for sure, but that and a laser is about as far as I would go with "accessorizing" that weapon... or any HD weapon for that matter.
Cost of ammo isn't a factor for me, I do not have to be accurate to be lethal with a 12ga so I do not practice as much as I do with my CCW, but if I did, I'd want a fairly common caliber. .357,.45,.44 should all do pretty well.
What do you think is better to use? Please explain exactly why it would be dumb, and what would be smarter to use in its place and why.
Not to answer for the poster, but, 12ga. I'd chose it because the risk of ANY collateral damage is extremely low and I (meaning me) cannot acquire and neutralize a target faster with a rifle or more accurately with a pistol.