I started leveling as fire and it was taking longer when my crit started dropping as I leveled. I switched to frost and sailed smoothly up the levels. Frost bomb, frost ward(aoe)/frostjaw(single), nova, freeze, and the ice lance glyph to give it a cleave all gave me plenty of shatters.
If you mean Deep Freeze lance spam as your only good damage, you may not be using your full toolkit.
i cant seem to prefer one spec over the other. i switch every now and then. fire or frost. one tip i can give you is to use NETHER BOMB as frost. it will proc Frostfire bolt that will CRIT even if target not frozen. it helps A LOT!
as fire - i just open with Fireball or Pyro, and then scorch and wait for crit, then inferno blast + instant Pyro + possible combustion(overkill)
Note: only the last applied bomb has a chance to proc Brain Freeze, which means you can spam Nether Tempest all you want, but it won't guarantee a proc. On the other hand, you might get 2 procs. However, Frost Bomb guarantees a proc and does great aoe damage.
For leveling I used Arcane and it became a lot easier when I got into the mentality "I have lots of buttons, must use them all." People often don't do that thinking "this is a powerful cooldown used for bosses, I won't use it on some mobs in some zone that I need for quests" and spells like Arcane Power go to waste when they'd help immensely.
I started as frost, found it got really slow to kill stuff around 87, and switched to fire/arcane depending on what I was doing. If you are doing fire, switch to frostfire bolt instead of frostfire and it'll slow. Spread combustion and the stun from Dragon's breath make short work out of groups of critters.