So far, I've got 7 transmute spec (I'll have 19 when it's all said and done) high enough to do the living elements transmute, and 2 high enough to do puregold. In my opinion, with enough transmuters, the living elements is the best bet. I've been buying lifes any time they're less than 10g, and airs go for 30g consistently on my server. I just send my characters down to Uldum, and hearth back home. So far, in the 4 or so days since I started leveling professions, I've gotten 2 procs from doing airs. One was 14 earths (~15g ea) and one was 16 waters (~12g I think). So, napkin math time:

(we'll go with 5 transmuters, as with blbjtb)

750g for 75 lifes

those turn into 2250g without procs

1500g profit for 5 toons doing airs, and I've had them sell as I'm posting them. Truegold won't always sell immediately with people undercutting you.

with procs, it can be an extra 150g or so per toon/proc.

I'm going to stick with airs until either lifes go up, or airs drop.