Balance/resto or shadow/disc for casual world/bg pvp

I'm going to be rolling a new toon with some friends soon, with the end goal of being casual pvp alts, as in random bgs and rp world pvp. I like caster pvp much more than melee, but I'd also like to be able to heal due to the ability to share some gear. Thus my choices are a balance/resto druid, and a shadow disc priest, as a currently raid on a ele/resto shammy. I'm just wondering how each of those combinations are doing now, and maybe a bit about playstyle. For reference, I play/have played an ele/resto shammy and frost/arcane mage.

Thanks!