ok this is from a PoMpyro mage so may not apply to everyone.

It depends on how much spell dam you already have. if you have 1300+ dam (arcane/PoMpyro) or 900 (fire) then yes the haste is better,BUT if you have 600(arcane/PoMpyro) or 300 (fire) then no.

remember haste is a damage modifier, it doesn't increase your damage per spell,only decreases the time it takes you to cast your spells,thus giving you greater returns the higher your +dam is....that being said the faster you cast the faster your mana will drop. the more haste you have the more mana you need.
i currantly have 15k mana raid buffed..i dont suggest going that far but 12.5k raid buffed is minimum for caster endurance.

now all that being said the single best damage modifier is +spell hit (not spell pen= useless in pve) if you are not hit capped do so you will see your greatest damage increase here.

NOTE: i did not include frost above why?...its useless once you hit 70 and start to raid,UNLESS its talents are used to enhance other trees like fire or arcane, namely icy veins for more haste.


i find the above to be true through my game experiance,not everyone will agree. if it makes since to you cool. if not and something works better for you also cool. just trying to help out