Remington 887 NitroMag
I picked up one of these today for home defense purposes. It got a great deal on it so I figured what the hell. I loaded the chamber with a 3 1/2 in #4 load and the rest in the tube are the PDX Slug/Buck combo. I have only fired 20 rounds out of it but I was impressed. It patterned well but its light weight made it slightly recoil heavy. Overall I liked it pretty well.
You couldn't pay me to shoot a 3.5" shell in one; 3" are bad enough.
For HD I would stick to 2.75" so recoil does not get in the way of HD shooting, if you have to.
The tube is full of 2 3/4 the only monster in the gun is the one in the pipe. The recoil is heavy but I feel like the 2 ounces of #4 is worth the recoil. This is strictly my shotgun, I picked it up because my wife stole my 870.