I love my Mossbergs and H&R's. I have killed loads of critters and Deer with my Mossberg. It is great for birds and clays. But I have not had a new slug barrel to compare to a H&R Ultra Slug. I tried using a couple used slug barrels on my Mossy with no luck. Could have been I did not try enough variations of slugs. On the upside. I have killed every Deer inside of 75 yards with my vent rib barrel bead sights that I have ever shot at.

This last year is the first time in many years my Mossy did not go Deer hunting. Only because I now have a H&R .357 Maxi

I do have an Ultra Slug 20. Very accurate! See profile pict

I know one fellar with a tracker. He will not hunt Deer with anything else.
I do know guys who use the Mossberg with slug barrels with great success. Mine was just bad used barrels or like I said, I gave up before finding the right slug.
If you shoot inside 100 yards I say go with the Mossberg. Then save the funds for an H&R rifle if legal in your area for deer.
Lonny
PS In my opinion, you can not go wrong with either.