Get a Jellyhead .660 for the 870 if cost is a factor. If not then try a Pure Gold or Rhino and then order a box of Nitro Shells, all for the Beretta. The Jellyhead is not only reasonable but is a solid shooting choke too. The Rhino is a definite step up.
The XR, Hevi13, Hevi Mag Blend, and Nitro are all in the same price range. Nitro isn't as widely sold because they are loaded to max powder levels. Having shot all 4 brands I can tell you there is a tremendous difference in them and the cheaper copper plated 5's.
If you go to the Nitro site they have a recommendations page. They have shot a lot of gun/shell/choke combos and can suggest something. I found that the Mag Blend and Nitro have very similar patterns in both my 870 and SBE II.
Last edited by bald9eagle; 02-03-2015 at 01:21 PM.