I've listened to high, mid and low efficiency systems that sounded great. Horns are waveguides, so they have unique sonic properties. Whether you like them or they work well in your room is a personal choice - listen (to good ones) and see. Horns are complex and easy to do badly, moreso than some other sorts of designs, so QoI is a great concern with them.

Also, in bass systems efficiency = size, (generally) so that is something to think about.