Lennox Lewis was better, he fought a lot more dangerous threats in their prime, and he ko'ed most of them.

Calzaghe is a great fighter, but Roy land a lot when he threw, I think his biggest fault is he didn't follow anything up, in his prime Roy didn't just potshot with one punch, he would do it from time to time, but he would mix in combinations as well, and he would go to the body.
Hesitation or lack of reflexes he once had were why Roy wasn't getting off.