Priests (of any build) are the best class for taking down a paladin. This is done through patience and repeated use of the Mana Burn Spell. Start with a burn (or fear if the paladin is on you), then immediately dispel twice.  The pali’s buffs are magic and easily recast, but if the pali isn’t paying attention, they will not. Afterwards do not stop Burning them until they are out of mana.  Then begin Blasting/Flaying them until they are dead.  Do not bother DOTing the pali, as they have a cheap purge spell.  When they put up their shield and heal, use it as a chance to bandage. If they try to cast a spell without their shield, silence them, it’s a heal.

Paladins can deal next to no damage, but take a long time to kill. Sit back, relax, and feast apon thier fan boy corpse.

Any priest build should kill a paladin 99% of the time unless interupted.