I don't like to change targets, so I just heal whoever I need to:
/cast [target=focus-target, help] HealSpell
/cast [target=focus-target-target] HealSpell
The first one heals whoever I pick or if someone is outside the party (BG). The second one heals whoever has aggro. No thinking about anything, just heal whoever is getting beat on.

For round-robin-ness:
/castsequence [targe=focus-target, help] HealSpell
/castsequence [target=focus-target-target] HealSpell
Next:
/castsequence [targe=focus-target, help] , HealSpell
/castsequence [target=focus-target-target] , HealSpell
next
/castsequence [targe=focus-target, help] , , HealSpell
/castsequence [target=focus-target-target] , , HealSpell
next
/castsequence [targe=focus-target, help] , , , HealSpell
/castsequence [target=focus-target-target] , , , HealSpell

I would at least mention that my pally team has a shammy in it. Strength of earth totem, tremor totem, auto-magic disease/poison totem, healing stream, etc do SO much more than the 5th pally.