I think my friend Ed Head has the best AR "house carbine" I've seen...essentially it's a short-barreled AR stripped of all the frippery and fitted with a white light, a sling, an Aimpoint Micro and a Surefire Suppressor. It's sighted in for 15 yards and designed solely for home defense. I'm working on an old carry handle M4 copy AR for a friend who wants exactly the same thing, but is happy with his irons. Light, fast-handling and simple; the only accessory a light on the front. My own house rifle is a Spike's Tactical fitted with an old military Aimpoint and a Streamlight mounted at the 6PM position. That gun is sighted in at 25 yards, verified at 50, 75 and 100 yards.
The operative words for a house rifle are light-weight, no frills, a mounted white light (because rifles take 2 hands to operate, so if you have to search you have a light on the gun), and either irons or an ultra reliable red dot. An extensive rail system just adds weight and doesn't buy you much. The plain vanilla M4 carbine configuration is excellent in this role.
The best commercial rifle to fit this model is the just-released DoubleStar Constant Carry Carbine (C3). I haven't had a chance to shoot the gun yet, but I went though all the design parameters for the gun with Don Alwes, DoubleStar's chief trainer and a good friend. He sees the C3 as his vision of a patrol rifle...you're not going to take it to Afghanistan, but then again, you're not going to Afghanistan, are you?
For 3-Gun, it's no secret that JP Rifles are among the best in the world, and are priced accordingly. I shoot a JP, and it is a far better gun than I am a shooter. The amazing thing now — assuming we survive the current war — is the plethora of 3-Gun ready rifles. My Sweetie is shooting a Stag 3G and it's a heck of a gun, especially at the price point of roughly $1500. Her only complaint is that it is a little over-comped, that is the compensator is too efficient and brings the gun back down below horizontal on recoil. Before the new season starts I'm going to replace the Stag comp with a Miculek comp.
I haven't shot the new DoubleStar 3-Gun rifle, but the one I handled looked spot on. I'll shoot it Monday on DoubleStar's 3-Gun stage at media day. There are any number of specialty 3-Gun rifles...the Noveske is magnificent, and my good friend Mark Passamaneck at Carbon Arms builds a wicked competition rifle. I have a proto Ruger 3-Gun rifle built by JP that is sweet...we've never done video or stills on it, which we will this spring assuming we all get through this. You'll also see the Ruger on SG 2014.
Note that the 3-Gun dedicated rifles are relatively heavy...makes them perfect for when you have to carry the rifle for no longer than a couple of minutes or you're using them for prairie dogs or coyotes.
Also note that Stag, DoubleStar and Ruger are sponsors.
For a tactical class rifle, I say love the one you're with. I've run classes with a baseline S&W M&P and a baseline Stag, and both were perfect for that. Not as light as a dedicated house self-defense gun, but a couple of pounds off the beefier 3-Gun beasts. If all you've got is one AR, use that one. One thing I want to do this spring is take (and film) a carbine class — hopefully one of the Magpul Dynamics classes — with a .22 LR AR. My off-the-top-of-my-head plan is to use my old Tactical Solutions conversion unit that's semi-permanently mounted on a Stag lower. I have lots and lot of rounds through that rifle, and I have enough CCI Tactical .22 in stock to get through even a long class. I just pulled my Millett DMS 1-4X off the FAL and put it on the TS/Stag .22 for 3-Gun practice, so that's probably the configuration I'll use.