Well, with 5x Shammies, you can experiment.
For battlegrounds, 5x Fire Elemental or staggered... with a 5 min cooldown (glyphed) is quite nice AoE power, especially if you are swarmed.

As you pvp and gain honor, and buy gear (wait until the next season starts, and its better gear for the same cost), your resilience goes up, which is staying power.
With 5x Shammies for heals + healing stream totems, you become quite a force.
AV is generally a really good BG; a lot love EotS too.