I don't think the team suffers much of a drop-off on defense, or in terms of rebounding, when Oden is in versus Przybilla...with one important caveat: fouls. Fouls, beyond limiting Oden's time on the floor, are damaging. And Oden is certainly worse than Przybilla in that respect. Beyond that, though, I think Oden is a slightly worse individual defender but a better team defender (I think he closes off the lane to opposing slashers better). Przybilla is a slightly better rebounder, but both are elite.
So Przybilla may have the very slight edge in terms of defense/rebounding, but Oden has a massive edge on the offensive end, IMO. Oden draws double-teams quite a bit, while Przybilla doesn't. Both are high-percentage scorers, but Przybilla's scoring comes almost exclusively from put-backs or broken plays. While Oden gets a fair number of put-back baskets, he's much better able to create his own offense. Oden is just a much bigger offensive presence, and I don't think the gap between the two players on defense is anywhere near as big.
So, I think Oden is a better player than Przybilla. But consider that Oden doesn't replace Pryzbilla...he takes minutes away from Frye/Randolph, largely (and maybe a few from Outlaw). So, the question is really Oden versus Frye/Randolph, when comparing the team with and without Oden. And Oden is so much better than Frye/Randolph that it's very obvious (to me) that Portland is a much stronger team with Oden, even if it is arguable as to whether Oden is superior to Przybilla.