Check for your server on theunderminejournal.com (thanks for the link btw, Newbie916. I love it already).
for my server, Truegold sells at 120g profit at the moment. So over 12 alchys, 1440 for Truegold vs 1600-1800 for Vol Air.
But mostly for me its that I can sell Vol Air much easier. List 18 stacks of 10 and come back the next day and it's sold, whereas Truegold is a never ending undercut fest.