Ancestral swiftness is pretty much the worst talent out there for us. I don't think we've really discovered any fight where it's beneficial. It's mostly a resto talent so they can drop an instant heal if they want to. Could also be used for enhance for back to back lightning bolts though.
Echoes wins out over all three theoretically, but EM will have it's place. It has a 6% proc chance for us, and IIRC Blizzard basically said it had no ICD except a small enough one to make sure back to back procs aren't happening, but not big enough to notice it.
Elemental mastery is an ability we can take if we want more burst, the problem with it is that ascendance is our burst talent (paired with FE). If you're a troll then elemental mastery doesn't give much of a benefit during ascendance besides stacking tons of haste for flame shock ticks.
For non-trolls elemental mastery doesn't line up with ascendance so that kind of sucks, but it is still going to be helpful. Still, as we gear up the value of haste during ascendance goes down. Off a guess I'm going to assume that haste is going to really drop in value sometime in T15 just because we'll have enough of it to the point where everyone is 1 second capped in ascendance. It will still be beneficial outside of ascendance, but looking at stat weights now (they will vary from player to player) but all three secondary stats are starting out to be pretty close in value with the general rule of haste > mastery > crit.
Since haste is going to eventually stop being as effective in ascendance, mastery affects the vast majority of our damage (in and out of ascendance), and crit doesn't affect a little over 50% of our damage (not to mention none of our damage in ascendance) we're eventually going to see mastery pull ahead of haste further into the expansion.
That's my guess at least.
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