Voted Joe Joyce since he's listed twice. Plus he badly hurt and stopped super tough and durable Joey Parker.
He hits hard, but imo it's more accumulative thudding power, not one punch knockout explosive power. In pure one punch explosiveness I think Joshua hits harder.
Zhang's straight left might be the hardest punch in boxing. Powerful short right hook as well. Wilder's power still on another level though.
Joyce, it has to be. He really punches through the target better than anyone currently, bar Wilder. Plus he stopped possibly the best Joseph Parker we've seen.
I would guess The Makhman. Joshua being a very close 2nd. But honestly Murat Gassiev hits harder than all of them. Much better technique too