Depends on the gun and the use....
For bolt guns used for longer ranges, a 1" tube Leupold 4.5-14AO preferably with the VH recticle. Second would be the Shepherd 3.5-10x40 AO....
Semi-autos, pumps and lever guns will often get the Leupold VX-III 1.5-5....
Wish that someone made a QUALITY 3/4" tube scope like the old Redfield 4X..... That would be perfect for the Marlin 39 and Winchester pump guns....
Bob