Propane is the most expensive option to operate. It is a lot more than gas. Solar panels are the cheapest to operate if you have a good sunny southern exposure. Heat pump is cheaper than gas to operate, but slow to heat. If you are looking to maintain a steady temp or heat a couple of days for weekend swims it will work. The climate in GA is probably good for a heat pump. Especially using a cover. I would get a big one, you have a big pool. 140k btu or thereabouts.
I would get Pentair because that is what you already have and they make good stuff. You could get a Suntouch down down the road if you wanted some automation, especially if you decided to add solar too. It could control heat pump, solar, IC60 and the pump.