this kinda question is wot makes boxing match ups puzzling
it boils down to styles make fights some boxers are more at risk from hooks ( tyson ) or crosses ( lewis )
id probably say prime Tyson hit harder but when he lost his speed then i think the 34 year old plus Lewis hit harder because he carried so much bulk.

I remember after Larry Holmes had fought a prime tyson he said people hit harder , even though Tyson was the first to KO him , this is down to Tysons speed and the pact that he was a slugger.
cheers chaps !! thats my opinion