RE: shotgun scope?
For a shotgun shooting slugs, your two most important features are going to be durability and eye relief. The former to keep the scope working properly after many rounds of heavy recoil, and the later to keep your forehead relatively clear of marks that suspiciously resemble the occular end of your scope. For slug gun ranges, I wouldn't bother paying for magnification above 4x or so.
I have a Bushnell Banner 1.75x-4x. Not sure of the objective size off the top of my head, but the little sucker has 6" of eye relief and seems pleny clear. I didn't do much research on scopes before buying it, but it's been working just fine for me.
Good luck, whatever your choice.