I think you can check this out on their official web:  http://www.mozztalk.com/
Among the algorithms, HEFTY1 is the best one to resist ASIC and FPGA at present. HEFTY1 parallels with four algorithms, which increases security. (X11 connects 11 algorithms in series, seems to use 11 locks to lock one door, and door will be open only with one key.) That is the reason why we use HEFTY1.

they already answered this question on general discussion, FAQ