Towelroot will only work if your write protection to the sys partion is turned off. It will most likely never work on stock b/c of this write protection unless geohot can somehow bypass it.
HTC One M8 running stock(current)
SGS III running Quantum by pwncakes (old and sold)
Moto Atrix 4g running Neutrino(older)
Samy Captivate (paperweight