What version of season 14 PvP gear should I focus on for a lvl 90 Holy Priest?

Holy/Shadow lvl 90 Undead Server Arthas

I am returning to the World of Warcraft after several years. Many, many things have changed in the game and I am hopelessly trying to play catch-up. Most importantly is getting up to snuff as a PvP healer. So far, all I manage to do is tickle my teammates with my heals. I have looked into Tyrannical Gladiator pieces, but I've noticed there are quite a few changes to attributes.

I usually queue up for random battlegrounds as I want to maximize the frequency of getting into one. I tend to heal more with AoE with [Chakra: Sanctuary] enabled.