Honestly what surprises me about enhancement shaman sims is that if haste is dependent upon what "gear" you have why isn't there a set haste or even a soft cap for gear sets. Most shamans that are consistent enough that have at least a 4 set of T9 by now it would depend on off items (ie belt, boots, bracers, trinkets.) Whenever i am bored i go on wow-heroes to look up all the top enhancement shamans on my server (im in the top 10), and top servers i know of to see if there is an over all consensuses on haste or Ap. Surprisingly enough Ap is the most commonly used gem with yellow slots being taken by 20ap-10haste. Over all the argument between which is better haste or Ap seems to come down to a preference for the player. Going over a lot of charts that i have seen from enhsim, people with matching gear stacking Ap or haste honestly do not vary that much. As everyone knows who posts on these forums Ap increases Sp which makes are rotation attacks hit harder, but slows us down some what. The mirror is haste which speeds our attacks up and allows for more MW procs and more white dmg. Thinking literally without simming, you can assume that they would actually even out in the end.
Basically what im getting at for everyone who cant read topic posts stating to stop asking what one is better for your enhancement shaman. Its a preference, if you feel the way for you to go is more MW procs and a shit ton of white dmg GO FOR HASTE! If you want massive dmg from your over all attacks(SS,ES,LL,WF) then stack AP. We are the most complicated class theory craft wise, which is why here on MMO and on elitist shaman forums are one of the most flooded topic discussions.
This is again just my take from what i see, im sure there will be plenty of trollers and i welcome all of it. <3