I have:
Pally
Mage
Mage
Warlock
Priest

I use my mages+warlock for Blizzard AoE grinding, so Frost is the way to go.

However, if I had 3 mages, I might go AP+Pyro to knock out-blow on single targets.

Knowing what spells to use isn't as important as knowing how you want to setup your Macro system. The big debate now is Focus - does Focus follow your "Leader" or does focus follow CC. That's an important consideration once you get out of Northshire Abbey (or any other starting zone).

Right now, I have Focus following my leader, and that truly changes every single macro I have [target=focustarget] is always the first thing there in a cast sequence.