It's user preference.
Sure they are more efficient but to the very good ear, Class a amps and maybe even a/b would be better for more realistic sound reproduction.
I can't tell a difference but some people can.. supposedly.
Most Class A amps are used for the ultimate in SQ goals and Class A/B high current amps used for subs aren't really a wise choice unless it's for SQ goals and the user can actually tell a difference between the two technologies audibly.