I have the leupold shotgun 2-7 on mine.

That's what it's designed for, 12ga slugs....

Have a 1.5-4.5 nikon on my other 12ga, holds up fine, wanted a little more power than the 1.5-4.5 though on this setup especially with the newer faster slugs out there....

I think the 2-7 is ideal, I'd also get a nikon in the future, my leupold power adjustment is crazy tough to adjust.

I'd probably suggest getting a nikon slug scope in 2-7 or 3-9 if you're set on that power range.

Either way I'd get a shotgun/slug scope, parrallax is typically set to 75yds, instead of 150 or 200yds like on most rifle scopes....and on a slug gun 75yds is perfect. Since about the longest shot anyone would take with a slug would be around 200yds.

So first choice, Nikon shotgun 2-7x
2nd choice, leupold shotgun 2-7x