Most of the top pvp streamers think spriests are currently the most op class/spec in the game, i dont play one myself but i do play a lock and they arent good right now. So based in my personal experience with locks and the opinion that pro players have on spriests, i have to say priests are better right now by a long shot. No need to mention warlocks are getting nerfed in 5.2 and spriests are not being touched.
Id give locks a 6/10 in pvp
SPriest 9/10 not 10/10 because they are always oom, thats their only issue.