RE: best slug guns
If you already have a shotgun for bird and small game I suggest getting a dedicated slug gun for deer hunting. You can get deer only pumps from just about every maker. However in most cases they will just be a regular pump gun with a different barrel on them. Not a pinnned barrel with a better trigger. And for the money they would cost you could get a H&R Ultra with a really nice scope or the Savage.
As far as the barrels alone, they go for around $200 for either the mossy or the 870 if you are getting the barrel alone. I am pretty sure you can get a slug barrel for your gun you have now, I just don't think they are very cheap is all.
I do believe Ithaca makes a deer only pump gun, but I'm not sure to be honest and I couldn't tell you how good it is. You would have to do some research. I rarely see them in any shops I go to, I know that.
I did see a 870 laminated stock version with a deer barrel on it in a local shop. Looked pretty cool actually. However remington doesn't list it on their website. I am sure it is just a regular 870 with some fancy wood though.
Paul