If you're seriously PvPing, I don't see much reason to take a pally unless you're really trying to make some sort of large target who can simultaneously function as a damage sponge and heal the rest of the group. Seems more trouble than it is worth.

In a PvE group, paladins make decent enough tanks, or main healers if you put a shadow specced priest in the group for minor aoe healing/mana regen. The 4 priest and a pally group would be an interesting looker just for the huge holy damage buffs, the lack of resistance factor for holy damage,and the fact the pally would be nearly impossible to kill with 4 renews ticking and flash heals.