Most energy efficient pool pump replacment

My old 3/4 hp pump had died after many years of service. My pool is 16x32, 3 ft deep to 6 ft deep. The old pump is a 3/4 hp marathon. I live in central Florida, the pool faces south and receives full sun until 7PM in the summer. The power company offers no price differential based on time of day and I have been running it 8 hr (9-5) per day. The pool has almost no one swimming in it (it came with the house). I need to minimize the electric costs of running the poo,l so what would be the most electrically cost effective replacement - single speed, variable, or two speed?