The savings from a 2 speed pump is HUGE. In typical installations, on LO, the pump moves about 1/3 of the water with 1/10 of the electricity (3x increase in efficiency) Also, filters function better with LOW flow, than with HIGH.

VS pumps save a little more, but are more expensive, more complex, and usually work best with electronic pool controls . . . which are ANOTHER point of failure. I'm not a huge fan, for simple pools.