I won't deny it. I am a huge fan of the H&R USH. There are FIVE in my locker right now, although one is my nephews.
Additionally I am, I guess you could say, really anal about well placed shots. If I'm not 100% confident I can put a lethal shot on a deer - I ain;t taking it. Hence I have no issue with single shot slug guns.
That being said, any well placed shot with a 20 ga. will kill a deer. I prefer the 12 myself because the bottom line is - it delivers more energy and plain out hits harder.
All of our H&Rs are what I would consider tack drivers.
Yes the 20 ga. is lighter than the 12 ga. but if you pull the dead weight out of the stock you will lighten it up quite noticably.
Also there are several options as related to weight. A standard USH weighs like 8-9 lbs as delivered. There is an Ultra Light Slug Hunter weighing in at 5 + lbs.. And an USH Compact (20 ga. only) at 7 lbs..
One thing I strongly prefer is the longer front stock like this ..........
As opposed to the shorter front stock like this ..........

Reason being you don't want to find your hand wanting to be right where the sling swivel mount is. And one thing you definately don't want to do is butt your forward finger up against the swivel mount when you fire -
believe me.
I'm a big guy with long arms/reach and I have totally removed my forward swivel mount. (I have my sling around the barrel and it can only be barely
squeezed off when the gun is broken open.)