This is just for fun and I know it would depends of the caster but in your opinion, what mage spec do you consider it is the strongest overall?
I personally Believe it should be arcane since it all about raw Magic which has more potential and/or applications.
Bonus question: what about warlock? Which warlock spec would you consider the strongest as well?
Arcane is power in its purest form and has the most versatility.
Essentially, Frost and Fire are both focused application of Arcane to create those types of elemental spells.
Arcane. Fire just burns the mana food, but no one wants ice cold buns either. Arcane’s got the balance right.
Well I would Say arcane until I met Jaina which makes frost OP.
And warlock, I would Say destruction
Anyone else? I would like to read more opinions 
I think in most situations, on average Arcane would be the most useful or at least the most versatile.
Any time you’re in an environment or situation where either spec would be better, however, Arcane would be completely outclassed.
Fire will always be a more powerful source of destruction. Constructs, barriers, and impacts of magically created/infused ice will always be more stable/solid than Arcane projections and fields. Every discipline will have its strengths and uses. While Arcane would conceivably have the most strengths and most uses, what Frost and Fire offer is more intense strengths and more potent uses for their respective applications.
Yes, I know it’s a very middle ground “balanced” sort of answer, but if there was one element to rule them all in Lore, the other two options wouldn’t be as significant or prevalent. There has to be concrete reason for these three disciplines to be the three main magical disciplines among civilized mainstream magic practitioners.
Interesing answer. I agree with you 
I’d have to say ice because of Jaina.
But if going by Khadgar all three are equal.
Personally, I think all 3 have different balancing elements which make them roughly equal. Individual skill would be the deciding factor.
Warlock-wise, I prefer Affliction; slow and steady wins the fight, I mean race.
Queen Azshara is an Arcane Mage.
I thought Azshara was a destruction mage
for me its arcane magic in the hands of a very spatial demon hunter
Arms Mage obviously.
Arcane is the basis of all mages magic. So at its core arcane is both the weakest and strongest, it is all magic. Fire and Frost are manipulations of arcane energies into fire or frost. There have been plenty of occasions were each of the schools are presented as the most powerful, but I would state it this way. If you are looking for raw magical potential, arcane wins out, because you don’t have to mold that power into another form so you can focus everything into a more powerful spell. You can trade off heat or cold for more power, and accuracy and control for more power, what this end result is or what it could do is not likely wise to experiment with, ut it should net result the most purely powerful spell possible.
arcane. as Rea already stated.
Usually depends more on the individual mage not the school. Also, unlike the spec mechanics, lorewise there’s no reason you can’t use all 3.
However, i’d say arcane probably cause in addition to the raw power (which all 3 schools of magic have) it has a wider variety of utility such as portals/teleports, polymorphing, as well as time magic and clones.
Though I suppose from a lore perspective some of those things could be considered their own categories.
Azshara aside, I think the devs’ answer is “human”
I would love to see that
fel mage = warlock so…Frostfire is my pick.