My biggest concern is ability to cool adequately in a hot/humid area.
Why the worry about that? The earth-coupled heat pump should do just fine in that situation.
We do/did have someone here who had a ground-coupled system that caused quite a bit of trouble. The theory behind them is solid, and many people have had good results. The issues tend to be initial cost (depends on how much it costs to establish the thermal link to the ground/body of water) and the small-but-essential details of the system. The person that had trouble here had issues of the second sort.
There are two major architectures for these systems: "Direct" (where the refrigerant used for the rest o the system is also pumped through the ground loop) and "indirect" (where a water/glycol fluid is pumped through the ground loop and a separate heat exchanger is used to interface that fluid with the working fluid in the condenser). The "direct" is simpler, can be cheaper to install, and theoretically more efficient. The "indirect" is probably the way I'd prefer to go if buying one, though. Digging for the ground loop is a major expense, and you never want to do it again. There are already new refrigerants on the horizon, and they may not be compatible with the present ones (just as the lubricants in R-22 systems are incompatible with present refrigerants, including R-410A). If you've got R-410A in the buried loop and it gets badly contaminated (chunks from the compressor, scale from poorly-done brazing of copper lines, etc) or is incompatible with the next gen refrigerant, your investment in that ground loop becomes worthless. If you've got a loop of water/glycol, you can use it with whatever comes next. Plus, I think a low-pressure water/glycol loop is just less likely to leak/cause trouble in the first place.
Unless I was planning to live in the house for a long time, I wouldn't consider a ground-source heat pump. The installation costs are high, and it's unlikely to significantly enhance resale value. In fact, it could put some buyers off. OTOH, if I lived somewhere with high heat/cooling requirements and expensive electricity, and if I planned to stay put a long time, I'd look into it.