I leveled my dual mages as frost for more survivability and very little downtime. That said, it really isn't going to make much of a difference, so just choose which tree you like most. You're going to two- or three-shot every normal mob with dual mages anyways. =)

For frost at level 24, I'd probably spec: http://www.wowhead.com/?talent#oZZAc0co If you start at max range, nothing except elites will touch you, and if they do, pop Icy Veins to cast through the attacks or frost nova + blink away to rinse and repeat.

For frost at level 60, I'd probably spec: http://www.wowhead.com/?talent#oZZAccIofu0fdMfox If you find yourself AoE'ing a lot, then I'd move some into Improved Blizzard. If you want to AoE grind a bit, go for Blizzard; if you just happen to get several mobs while questing, Arcane Explosion spam will suffice. Now that Blizzard can crit, having Frostbite is not really a big no-no anymore for AoE'ing. I would pass on Deep Freeze, although it can be handy in a few situations.

Keep in mind these talent builds are geared to how I remember playing frost mages while leveling. They may not be the best/optimal setup, but it worked for what I preferred (high survivabilty, low downtime, mostly single-target killing while questing). I did try AoE grinding for a while, and while it worked and was pretty cool, I just could not put up the XP/hour numbers that questing (while I had RAF bonus) could. Your results may vary though!

Also, remember with dual mages to stagger your Frost Nova casts. Make macros like these:
Main: /castsequence reset=24 Frost Nova,
Follow: /castsequence reset=24 ,Frost Nova
This way you can bind these macros to the same key. First time you hit it, the main novas, then the next time you hit it within the reset period (set this number to whatever your nova CD is) the secondary mage will nova. If you button mash, add more commas to the macros to account for that. Also, this set-up is useful for other spells like Counterspell or Deep Freeze as well.

Hope this helps if you end up going frost, but no matter what, just choose the playstyle you enjoy and tailor it to your personal preferences. Having dual mages is much more forgiving with weird talent builds and such because single-target mobs die quick anyways!