Most of today's scopes are very good, it comes down to what you want to spend.

On the lower line I would look into the Bushnell Trophy XLT, not a bad scope for the money, matter of fact I have one on one of my shotguns.

Nikon Pro Staff are very good I have one but not yet mounted on anything.

Votex Diamond are really coming up strong

Leupold VX-1 is good quality with Leuopld's Name backing it up

Leupold VX-2 well just a damn great scope I have them on many slug guns, and would say that is the scope to look into and purchase

Whatever scope you go with I say go with a 3-9x40 with a plex. No need for a "shotgun only" scope, todays shotguns and ammo combo can reach out further, and a rifle scope is what you need