I was a frost mage my entire WoW career up until about a week ago when I decided to give fire a try. What it boils down to is this: "What do you want to do?". I can already tell you that frost or arcane spec is going to give you a much more friendly instance experiance. Arcane mind will give you a large amount of mana and points in frost channeling will decrease the amount of mana your forst spells consume. Frost is much cheaper on the mana pool to use. Also in instance such as BWL, you will run into many encounters where the boss of the instance is immune to fire. Vael, Firemaw, Ebonroc, Flamegor, and Nefarian are all 100% immune to fire. Molten Core isnt as bad, however 90% of the mobs in there have high resistances to fire based attacks. So, if you are looking to top the damage meters in these instances then frost is going to excell over fire.
If you plan on spending most of your WoW life PvPing, then fire very well might be the way to go. As a fire mage you will hit hard and have a large amount of burst dps. First of all Combustion, the 31 point talent, is useless. The most popular fire spec would be 30/21 Fire/Arcane. This will allow you to instant cast pyroblasts, which is much better than having a 100% chance to crit for 1 shot.
There is also the factor of your gear. Fire mages and Frost mages look for different strong points in their gear. Fire mages look for a large percentage of spell crit in their gear. Frost mages typically look for large amounts of +dmg. The crit helps proc ignite, a must have for all fire mages. this will give a 2K fireball crit 2 ticks of 400+ dmg.
Frost mages are not to be underestimated as damage dealers. As a frost mage I could crit for 2200 unbuffed. However, that is with around +550 frost damage and is only achievable with epic quality gear.
Here are a list of some of my favorite specs:
[B/]AP/Frost spec (AP is great if you have the +dmg to back it up, no ice block is a downside but can be work around)[/B]
http://www.worldofwarcraft.com/info/cla ... 0000500000
Class is almost over but I will add more to this when I can, net is down at my house for an unknown reason so it might be awhile till I can get add to this.