I'm in New Orleans, so I've got experience with your climate. A high-efficiency heat pump is a great choice in our climate, far superior in efficiency to natural gas heat. (I'm not at all anti-gas, and I have two on-demand gas-fired water heaters and a gas dryer.) You want not just high SEER, but variable speed and inverter-driven, so the PW's can start the heat pump without any extra effort. If you're concerned about repairs to a variable speed, get a warranty. I'd also go with multiple systems, maybe one per floor. That way, when the one in your bedroom breaks, you've got other cool spaces in the house where you can sleep.
I looked at the Lennox XP25 to replace an old heat pump, and it's a great system. As others have said, a great installer is more important than a great system. The Lennox is too big for my space, though, so I got a Daikin Fit instead. I LOVE that unit -- the exterior is small like a mini-split, mounted high on an exterior wall, but it uses a conventional air handler and ducts inside. Speaking of ducts, do NOT put your ducts and air handler in a hot, unconditioned attic. And do not use any powered ventilators in an unconditioned attic -- they make almost everything worse, but contractors still think they help.
If you can find a roofer who's not doing roofs the way they were done 30 years ago, be sure they put 3/4 to one inch of rigid foam board outside of the roof decking, over areas that are conditioned like a conditioned attic or cathedral ceiling. That will eliminate most of the moisture/condensation/mold problems that tight new houses can have in our climate. But almost no one knows how to do this. And a n integrated dehumidifier like a Santa Fe will make the house much more comfortable.