You have to build for what you are doing. Your nukes scale better with +dmg than most of your other spells so you need to figure out how you want to grind. AoE grinding with mages is the best exp/hour bar none in the game. Unfortunately, due to the huge overpopulation of the server, it's pretty much practically impossible at this point. Maybe in the later game, but not anything before 40 I can tell you that.
AoEing
If you intend on aoeing, the only things that matter are stam and intel. You have to have the stam to survive the beating you're going to take while you gather the mobs up, and a shit ton of mana to cast enough expensive AoEs along with FNs CoCs and Blinks until the mobs are dead.
Nuking
Nuking is good for single target dps. It's also the best if you intend on doing lots of dungeons since this is where your main dps is coming from. Since your nukes make better use of SpellDmg it's highly valued, and enough of it will significantly increase your dps. Stam isn't so important on trash as you'll have the mobs close to, and in later levels, dead, before they even reach you. However, you'll also have to worry about longevity, and even at high levels, you'll still only be able to do about 3 mobs before you're on your ass drinking (more on this later). Now here's the thing, and it's what Chainsaw was trying to say above, albeit, not very effectively. Spell damage = Mana (Int.) The more damage you do, the less nukes you have to cast, aka the more mana you save. There's a tipping point there somewhere, but that will change depending on what level you are so it's not even worth theorycrafting. Baasically, after level 30, Spell damage becomes much more valuable, and maybe a tad earlier for frost.
Stam vs Intel vs Spirit
I talked about stam in the beginning, and the short answer generally is stam for aoe, intel and/or spirit for everything else. If this was a pve server that would be the end of it. However, this is a pvp server, and you have to be prepared for ganking and in PVP Stam is king, so don't entirely neglect it. For dungeons, theoretically, it's very low on your priority list as you're not (supposed) to be getting hit. In reality, many of the so called "tanks" while leveling couldn't hold aggro on a mob if it sat on his face and you tied it to him. Spell power will only complicate this issue.
As for Int vs Spirit. That's going to change based on your level and spec. From 1 -20 Stam is going to be your priority stat. Mages are very low healthed and even low level mobs can be challenging. However, since you're working with mostly your base stats, your spirit is still very high in ratio to your mana and health, so you will regen them quickly, so pick intel over spirit. Prior to level 30, spirit will only do anything for you in between fights (unless you're arcane, again, more on this later) so it's value is limited. However, at 30, you get mage armor, which allows you to regen 30% of your mana regen while casting. This is practicaly mandatory in dungeons, although it's use is more debatable in the open world. Spirit will make this amazing as 30% of a low number is an even lower number, but 30% of a big number can be a lot of mana over the course of a fight. This ability more than anything, is what makes spirit work for mages. Don't undervaue it. This is the point where you'll have to decide to go for a tough mage vs a long casting mage for grinding, but for dungeons, spirit beats intel hands down.
Some personal preferences
Pro tip #1.
This is my third mage (not including the partially level mages I did on Nos and K1).I've forget more about mages than most people will ever know, and I'm still learning things about the mage. From the moment I rolled my first toon, a mage, 12 years ago, I fell in love with fire. The crackling of the fire and the roar as it left my hands...the smell of charred wolf and burnt kobald around the abbey...aah the memories. But I digress. Needless to say, I leveled my first mage as a full blown pyromancer, so leveling a nuker mage is certainly viable, but not the most efficient in terms of kills per hour based on downtime. My second mage when i rerolled Horde I was much the wiser and leveled it as AoE frost. While I'll concede that frost is a better build for leveling and much better for aoe, fire will always have a special place in my heart. My advice, spec for efficiency while leveling, play what you like at end game.
Pro tip #2
Arcane is the BOMB!!! People are infatuated with big numbers, which has most likley been the reason why AM have long been considered the worst of our nukes. But if you can get passed not having massive uber crits, consider this. The arcane tree has 2 very important talents, while requiring 10 talent points between the two of them is quite expensive, what they do for AM is amazing. The first one in tier 1 makes your AMs immune to set backs. While you can throw all your theory crafted dps numbers at me all you like, do it while that undead rogue/warrior/hunter pet/mob is bashing your face in while you're trying to cast a frost bolt at him. Likewise, use AMs on a mage/warlock/priest trying to cast nukes at you and see how well it works out for him and tell me about how poor it's dps is.
The second is in the second tier of the tree, clearcasting. Five talents gives you a ten percent chance that any damage spell that hits (resists are bad, take those + to hit talents) will make your next damage spell free. While for most mage spells this is rather meh, especially for five talents, there's two spells that makes this talent an amazing OMGWTFFACEROLLLULZ talent, Blizzard and AM. See, they don't just have the chance to proc CC when you cast them, but on each wave of Blizzard or charge of AM. This means on average every other AM will proc CC, but in reality, you'll get multiple procs in a row, which leads us to the next point. AM is a five second cast spell. Spells cast under the infuence of CC, don't count towards resetting your five second timer for mana regen. While you won't get your mana regen to kick in if you chain it AM, any proc of CC means you will have full mana regen while casting under the influence of CC. Add in mage armor and you're regening mana even while your not under the influence, and if you combine mage armor with an arcane talent further down the tree that gives an additional 15% mana regen while casting, you're regening mana at 45% while casting. Spirit starts looking really amazing. I get absolutely giddy while grinding when I get a "free" mob kill. I'll start of with CC up from the last fight, cast AM on the next mob, and CC will proc the entire fight, meaning not only did I not spend any mana to kill the mob, but I also regend mana at full regen the entire fight ending with more mana than I started with. Think about that for that minute you're sitting there downing a couple more bottles of fresh spring water. I'll literally just chew through mobs with clearcasting and AM with little down time. Certainly far less than with the other two nuking builds.
Damage from AM is also severely under-rated. of the three nukes, AM scales the best with spell damage, with over 100% of your spell damage (If I remember correctly). Put your first ten talent points into improving your AM and CC and you can maniacally lol at the frost mage in DM as he's wanding every boss and every other mob fight oom while you're still doing full nuke damage. If you've ever played an affliction warlock, you'll understand the concept very well. While an Aff lock will never beat a mage's damage in short mob fights, let him get those dots rolling on long boss fights coupled with their high spell damage coefficients, and superb longevity, and at the end of the fight all those small numbers put him at the top of the damage done meter. AM is pretty much the same. Think of it as a more powerful channeled mage dot.
It's not all sunshine and candy though, arcane does have a few downsides.
You'll take more damage with AM because the mob will have more time to beat on you.. I find myself having to rest more often because of lack of health than from lack of mana while grinding because AM doesn't kill as fast as other nukes. But it's much faster to regen health especially with a bandaid than drinking a mana bar back up. Spell damage will reduce this significantly, which has it's own issues taking us to the next point on the list...
+Arcane damage can be harder to get a hold of than frost or fire damage gear. Optimally, you want generic spell damage gear, unfortunately prior to the 40s,most low level gear is school specific, which rather forces you to stick with your chosen tree. While there is frost and fire damage gear in the early levels of tailoring, there is no arcane damage craftable gear and generic spell damage is non existent until the 40s. This leaves you with searching the AH for +arcane damage greens, which considering how everyone 'knows' that most mages eschew the arcane tree for damage, can be rather harder to find than frost or fire, although not entirely impossible. Still, with AMs spell damage coeficient, a few good pieces is all you need.
Use clearcasting wisely. CC works the best with AM and Blizzard. A free Fireblast, Fireball or Frostbolt is meh, and it's chances of proccing another CC is..well...one in ten, pretty low compared to AM. And whatever you do, don't waste it on a frost nova unless it's to save your life.
Don't neglect your other schools, in use or in talents. Resists are a thing in Vanilla, and there will be mobs where you'll have to switch to a different school than your preferred because of it, and it helps a great deal to have two talented nukes with which to pull from. Personally, while leveling, I prefer to couple with frost. In fact after 10 points in arcane, I go down the frost tree first. A frost bolt is great for an opening any time you don't have CC up to keep the mob off you that much longer conserving health, so the talent that increases your slow's uptime is great, and since your going to be more apt to use Blizzard over your other AoE's, a talented Blizzard is almost a necessity. And then the holy grail of frost, frost barrier negates a great deal of the damage you'll take while grinding significantly.
Well I hope that gave you some ideas and cleared a few things up. Best of luck out there and have fun! :w00t: