HHHmmm, never realy thought about it.. I have over 70 different species and most are Aphonopelma, mainly due to their availability in the hobby. But, my favorte would run a close race between Chilobrachys, Chromatopelma, Megaphobema, and Brachypelma.
I'm a huge fan of the Brachypelma. There is no other genus which combines good disposition, brilliant coloration, and a willingness to hang out in the open where you can appreciate them as much. You can get 2 out of 3 with many other genera, but Brachypelma has all 3 going for it.