I paid $340 for my H&R 20ga with the thumbhole stock in 2009. I shot six different slugs through it and got decent groups with most (3-5" for a 5-shot group at 100 yds). The best was Remington Accutips which gave me a 1 1/2" group at 100yds. That kind of accuracy out of a slug gun is as good as anyone can ask for.
I have no experience with the other guns you're looking at, but for the money, you simply can't go wrong with the H&R. As with any gun though, you just have to be willing to spend some $$ to find a slug that it likes. You'd be surprised how differently the different slugs will shoot out of the same gun. You can't just pick the first one you see off the shelf and expect your gun to drive tacks with it (unless you get lucky).
Good luck!