Well I've hunted with the 870 smooth bore for years, but i just bought a Ultra in 20 guage yesterday. I've read a lot of good stuff about it, so I'm really excited to take it shooting tomorrow.
If you don't mind the single shot get the H&R, I have one and I love it also in 20ga. You can't go wrong with the 870, if go this route get the rifled/cantilever barrel