Holy Paladin + Disc Priest would be vastly, vastly superior to dual priests as a double healer duo for PVP. With proper use of cooldowns, you would have so much more survivability in BGs then you would as a double priest team. I can't honestly say that I have tried to play multiple healers simultaneously in Arena, but if I had the inclination too I would definitely play hpal+disc priest and team up with a random warrior for 3v3

Also I think you would enjoy the paladin + priest combo more for PVE, as you gain the option to play both tank and healer