Grinding outdoors? Instances? Questing?

I could see Living Bomb being fun outdoors rounding up a bunch of mobs and letting them blow each other up. Not sure it would be the most mana efficient way (the more grouped into a pack, the more efficient), but would be pretty quick. Just need to find large groups of mobs that hang out together (seals in SE Fjord along the coast, scarlet basecamp just north of Naxx in Dragonblight, etc).

For instances, it would be tricky. Perhaps Frost as your main to slow groups down, then cycle through and Living Bomb them up. Sounds like a pain though, probably have quite a few deaths even on a good run. Edit: You'd probably have better luck with Arcane for Slow, just have each mage slow a different target and kite them around.

Questing could go either way. Arcane is best at single-target kills, but fire would do just as well. Just scorch once on main (ideally with Glyph of Improved Scorch) and fireball away.