I've played few BGs on my Spriest(tried one as disc but that was prolly the biggest mistake ever). I have not played any arenas yet since there's not a single 'good' twink on my realm. Active ones atleast. Not that I'd even like to, hybrid retardness.
From what I've understood. You have two option, assuming you're not playing gimbed class.
1. Go full offensive with either PvP Power or Main stat gems and pick few PvE pieces for extra socket slots. Pros: Your damage is quite ridiculous, you should be able to global pretty much every non resi stacking player. Also if you're hybrid your heals will be ridiculous.
Cons: You're still pretty weak even with base resi added, I've had rogues crit 9.5k with Evi on me, shamans critting up to 5.5k with Lava burst and mages totally destroy you with their 6k-7k pyros.
2. Go with max resi. You should never ever lose 1v1, 1v2 or even 1v3, if you're half decent. Especially against bad/average players. Good players might be able to kill you. But with resi gems you won't kill anything either.
Same shit in different package. Could even say that the burst is worse than what is was back in Cata. You might not drop from 100%->0% in a split second(as in there's actually time to react), but now there are multiple classes that can kill you in few globals.
P.S. Those who claim that 70s is more balanced than 90s, please go die in a fire. Ok, mongoloid oneshot macro cleave(read KFC) is beyond stupid.