Mastercam is BY FAR the best and most powerful I've used.

Then Gibbs. (Been using it since the Mac days of GibbsNC/CAD/CAM and Dos days of Virtual Gibbs)

Those two I know the best, with many years on each.

Then Cimitron. (Great for surfacing, haven't done much other type of work with it)

Then it's a tossup between things like Geopath, Surfcam, Bobcad and several other's I've used.