Variable speed pump or single speed pump?
A variable speed pump is a pump that is capable at spinning at different rpm’s. This allows the pump to pump water at different speeds. Running a pump at a slower rpm saves electricity. A single speed pump is designed to run at a certain rpm.
Variable speed pumps have several advantages. Running a pump at a higher speed is advantageous if you get behind on your chemicals, when you are starting up your pool, or if you have a water feature. These are all examples of great uses for variable speed pumps, but possibly the best reason is for the energy savings and the day to day maintenance.
When a pool pump is off, the water is not circulating, no chlorine is being added and the water is not filtering. Nobody wants to pay for a single speed pump to run all the time, but everyone loves how clear the water looks if your pump is always on. The variable speed pump is a great compromise. You can have the pump on all the time but at a low rpm and save a bundle on the electricity. Basically you can have your cake and eat it too.
A good variable speed pump is about twice as much as a good single speed pump. The energy savings will make up the difference. Pentair has a cool savings calculator where you can estimate your savings.
If you are going to build a pool, I highly recommend putting in a variable speed pump. Spend the extra money up front and benefit from the savings and the convenience forever.