Who would you favor over 15 rounds? Flowers was the better boxer, and would easily be capable of out-pointing Graziano. However, his biggest weakness was a soft chin, and Graziano had both the power and the finishing ability to exploit this. I'm actually uncertain as to how this fight would go.
If they fight three times each one goes 10 round. Tiger wins 29 of those rounds. But one time Graziano catches him. His chin was probably his biggest weakness.
On first glance Graziano with his power would look like a good chance over Flowers with his weak chin. But Flowers was a very big middleweight (spent most of his career at LHW) and Graziano's big KOs came against WWs and past prime MWs. Id pick Flowers to whip Grazianos ass and I dont think it would be very close. Hed slice and dice Graziano and win comfortably.