Been working on gearing my alt (tankadin) and managed to get both iLvl 200 waists from H. AN & Reg ToC. Those would be the Ancient Aligned Girdle & Girdle of the Pallid Knight, respectively. Do not plan on buying the heroism badge belt cause I rather just get the conquest badge one.
However, until I do that, I can't decide which of the two belts I want to use.
I'd honestly keep both. Pallid Knight will be for your MT set with the other for your avoidance set. While you say Prot is your offspec, most serious tanks carry various pieces of gear around with them for various encounters.
You'll use your avoidance/block sets for fights with a lot of trash or if you're in an OT role and the high EH stuff for bosses, generally speaking.
It's definitely a toss up and I don't feel like there's really a wrong answer to this question. Personally, I'd go with the Pallid knight waist, but I wouldn't frown upon anyone who chose the Ancient Aligned Girdle instead.