I have had a 2spd 1-hp Hayward SuperPump for 4 years now and will NEVER have a single-speed again.

I don't do anything fancy--there's a switch on the back of the motor for hi/lo speeds. That's enough for me.

My pool is almost 20,000 gallons and I run lo almost exclusively--even with solar panels. I have NO troubles with the skimmer this season, so if you do, check the line and any ball-valves for restricters. Last season I put in a new valve and it had a restricter so skimming wasn't good. Pulled out the restricter and it's FINE even with a skimmer sock.

High speed is if I really want to agitate the water, speed up the skimmer, backwashing and for the return side pool cleaner (the Dolphin is in the robot hospital..)

Definitely get a 2 speed. Get a higher quality pump and you'll probably be able to get one that uses elec more efficiently at hi AND lo.