I haven't shot many rifles yet, but the worst was either a S&W M&P15 AR, or a 30-06.
The worst kicking gun....?
My late 1910's Winchester 12 gauge model 12 with a round of buck shot. Walnut stock, no recoil absorber, that ole girl will kick your shoulder off! No bs, you run 3 or 4 rounds through it one after another you'll want to put it down.
My newer Winchester 1300 is a pellet gun compared to that model 12! I can shoot rounds of high brass BB steel shot through that 1300 all day no problem.. The model 12 will finish me after a few rounds