The store gave you an easy answer to a complicated question.
I think the softest shooting 12g semi is the Beretta Xplor now. For the weight of the gun, its is soft shooting, no matter what load you cycle. It's the 3 1/2" chamber model, original. It has a recoil system in the stock from the factory, gas operated action, and the forcing cone is less restricted.
Beretta's get internally grimmy, they are a gas operated recoil gun. Benelli is a recoil operated system, shoot it forever and just worry about inside the barrel.
The equation is gun fit to shooter, weight of the gun, and ammunition (load) plus all the techie stuff, recoil system and forcing cone restriction. The key is fit to the shooter. Bad fitting gun, more felt recoil, no matter what gun. Most of the US market guns are made for the average size right hand shooter.
All the above, a Stoeger M2000 synthetic with a few ounces of lead in the buttstock and a limbsaver recoil pad swapped in, shoots with about the same felt recoil of the Beretta Xplor using heavy dove loads and target loads.
Start with what fits you best, LOP, sight alignment, and cheek mount. If your walking around a half day or full day with the shotgun weight will matter after the first day. Sitting in a duck blind, weight is less of a factor.
