Maybe Doxxy ^
Anyway, I think Aveance and Membrain head textures are more expensive due the high quality and because they're very rare, since they don't seem to make those pieces of art anymore for quite a while now :o (Aveance returned a few months ago, but I don't know if he did that much).
There are lots of other good artists too. I can mention Chris, Jebus, Ferrock, Pate5, Vermine, Barreta, Yiazmat, 8OJ4N etc etc
If I were to choose one person, I'd say Membrain heads are more expensive/rare though.