Benelli: Supersport, Cordoba, Legacy Sport
Beretta: Any 391.
Barrel length- Whatever fits you the best. For O/U's I like 28'' barrels. For Auto and Pumps, I like 26'' barrels.
As far as ammo, the Beretta's will cycle lighter ammo better than benelli's but both should cycle 1 1/8 3 gram or better with no problems.
Good luck, You chose a two great sports.
Novaking