I'd recommend killing the corruptor tentacles that cast all those nasty debuffs first. While we can dispel most of the ones they put out, it's the ones that we cannot dispel as druids that are the real danger. I know the crusher tentacles debuff your damage, but getting debuffed to death is much worse than slightly lower damage output initially (the corrupter tentacles barely have any health, anyways). If there are any tentacles remaining once you get out of the brain room or transition to the last phase, same priority applies: corruptor tentacles first, crushers second.
As a slight aside, the corruptor tentacles have a level of 82, I believe. Therefore, they will have a decent chance to miss with their spells, allowing more time to kill them even if your damage is debuffed by crusher tentacles. All it takes is one plague to make your life miserable, so they're still priority.