Carnera is faster and more athletic. Valuev is more durable and has the better chin. Carnera seems to hit a little harder and throws more power punches with the intention of ending the match. Valuev relies more on a jab, and is rather tactical in his approach. Valuev to me has the better defense in terms of a higher guard and knowing when and how to cover up.
Carnera had the heavier hands, Valuev at this point looks like he is hard to hurt, Primo has proven heart, Valuev has yet to rise from a knock down or from being seriously hurt but he has not fought a Max Schmeling,Joe Louis or Max Baer either and John Ruiz,Ruslin Chagaev and the rest of his opponents have not shown the power of those 3
I think Carnera was the better fundamentalist, while Valuev may be a slightly better athlete. Its up in the air in terms of who wins in my opinion. A slow paced jabbing match over an uneventful 12 rounds is the likely outcome.