Extensive experience with air/air heat pumps in Florida. When the temp drops below 1°C you will need supplemdntary electric heat source, gets expensive. Best heat pums air/water. Need well down into freshwater table, powerful.in-well pump. You then need a means to disperse exhaust water. Cheap and effective to run, expensive install. There are no free rides.
You rarely will go that low in Florida so overall a heatpump will offer savings over resistance alone.
99.6% design temperature in Jacksonville is right around zero degrees. So less than 1 out of 100 days you will need backup heat in an average year.
Higher end heatpumps will give 100% capacity far below freezing but are not worth the additional price in many climates since temperature usually stays well above.
I live in north central Texas and have air exchange heat pumps. The actual units, and I have had them for 6 winters, do not use resistance electrical heat until the outside temperature is 10F (-12C). Of course, the units continue get less and less efficient, but they keep the house at set point until 10F, then the resistance electrical heat kicks in. At that point, the electrical meter really takes off. Still, I prefer this to propane heating.
I priced a geothermal heat pump and it was going to be 75% more expensive to install. I was very disappointed, as my parents had a geothermal heat pump for part of their house and it worked great in Indiana.