Warrior and Cleric or Warrior and Shaman

[Estu]

If your source of DPS is a warrior, you want to stay berserking. What a cleric offers that a shaman can't is complete heals and big heals, which are useless if you're berserking - what you want is small heals and regen, which a shaman can provide. Shamans also offer much better buffs, dps, and debuffs than a cleric for a warrior duo. Short answer is that the cleric duo will be far slower and less efficient than the shaman one.