Surely as a priest you are going to want more Int over Spirit so you don't OOM as quick?
Maybe this does not apply in raids where you will be battling bosses for long periods of time and inevitably you are eventually going to run out of mana, so spirit would be best.
But just for the sake of levelling up and dungeons, where you can drink every 10 seconds, surely you would want the INT so you don't OOM on camps/groups of mobs. You can just drink afterwards before the next pull?