AWHP v Ground Source (Geothermal), performance and cost – GreenBuildingAdvisor

All, typing a really long question to burn calories before the Thanksgiving feast. We are building a single story home in zone 6, 2000 sf, slab on grade, well insulated with ach50 goal of 1 of less. Doing in-floor heat for the slab (basically keeping the dogs happy) with ducted cooling and ERV.

When considering how to heat the water, the GC’s HVAC contractor suggested 3 options: AWHP (Entertech), Closed Loop Geothermal, or a combination on-demand LP boiler.  LP route is cheaper up front by 12k but not crazy about indoor combustion appliances or mechanicals. Ans with propane at $2.20/gal and Elec at $.155/kw, seems like long-term cost of LP would be high. Love the idea of both heat pump technologies but have never had either. And they both seem insanely expensive. So here are my questions:

1. Maintenance and durability: does either AWHP or Geothermal have an advantage? Seems like anything underground bears additional risks. He wants to put the looped piping under the slab and run it directly into the mechanical room. Says no way there could be problems, leaks, etc down the road with the no-pressure system he is using. Seems risky but maybe this is standard practice?

2. Cost: Both bids seemed insanely high, hoping to get a gut check I on cost. GC uses 1 HVAC guy on all his builds, no competitive bids.  Both systems came in at roughly 65k with AWHP being only 3k less than ground source, including all necessary components and install for zoned heating, cooling, erv, controls, pex and pex install, bathroom fan vents, dryer vent. Not sure why, I was expecting in the 50k range, and I expected the AWHP to be considerably less than the ground source. Without knowing all the specifics, and assuming equipment will be good quality, knowing you don’t see the bid and accounting for regional differences in labor cost, does this seem reasonable? 

3. For those with experience with both systems, any preference? Why?  

4. Bonus question: for ducted cooling and ERV, he wants to use r8 duckboard through unconditioned attic with r-60 cellulose sitting on top. Recent articles have me comfortable with insulating atop well sealed ducts in unconditioned attic but duckboard seems like a leaky situation. Anyone ever do this? 

Thanks to anyone who stayed to the end here. Any insights always appreciated.