jr,
If you are looking for a dedicated slug gun, for the money, its hard to beat an H&R Ultra Slug Hunter. Single shot, but you only need one:
http://www.hr1871.com/Firearms/Shotguns/ultraSlug.asp
I personally like the thumbhole stock, but that's me. Pick a red dot or scope you like, find the sabot that shoots best in
your gun barrel, and have at 'em.
As for slug, I like either the Federal Barnes Expanders or Hornady SST's from my 870, same from my son's USH.
Ask 10 people and you'll get 15 opinions on the 'best' slug....and they are all right, find yours.