If Walker is healthy, it could easily be him. I think he's a better player than Giddens, and we could use a small forward off the bench.
I think, though, that it will be Giddens, as others have said. He's capable of playing NBA-ready defense, and that's a skill we can use.
It will be hard for Pruitt to find a steady role with Rondo, House, Ray, and Tony getting most of the 1-2 minutes. Still, I think when he finally *does* get time, he could surprise some folks.
O'Bryant... ugh. Not expecting much this season. Maybe next.