For last year, I think the answer was Posey. For this year? I think it might be Powe.
At this point we all know what Posey brought to the table last year on the court (good D of 3/4, versatility to run small ball, clutch 3-point shooting). But to me, the biggest thing he brought to the table was championship experience, which gave him believability in the locker room that even the Big Three didn't have.
This year, the vast majority of the team has championship experience. We'll still miss Posey's on-court contributions, but the team no longer had as much need for what was (to me) his most important trait.
This year, what the team needs from it's role players, is to provide the energy to allow the team to win on a nightly basis over the long season without overtaxing KG, Pierce and Allen. To that extent, I think the biggest need off the bench this year is a jolt of energy and offense. And that's why, to me, Powe (and even Allen) may be better fits than Posey would have been. Posey himself is a vet that shines most in the post-season, so he fits perfectly on a young and energetic champion want-to-be like the Hornets. But Powe and Allen provide that young jolt to help get the engine running when the vets are on idle, as was the case last night for KG and Allen.