I'd really look at a Resto spec, if you want to play defensive.

Four resto, with essentially mana free Lightning Bolts.
Add in shocks, lava burst, 5-min fire elementals, and all the totems.
Not necessarily the blow_people_up powerhouse of Elemental, but not helpless when attacking.

And they have way more survivability.
Plus healing generally impacts BG's the most.
If you plan on going Elemental when you're geared, just use honor to buy the Elemental pieces instead of the Resto; the stats are mostly useful.
Depending on set bonuses, two pieces Elemental and two pieces Resto might be better than four pieces of either.