In our area the ground loop adds about $3,000.00 per ton to the
installed price of a heat pump. You will need to size the WS HP for
heating load, OR size it for cooling load and add backup heat for the
difference between the house heat load and WSHP heating capacity. If
humidity is not a problem in the summer, sizing for heat load will give
highest insatallation cost and lowest winter operation cost. If
humidity IS a problem, Size for cooling load; lowest installation cost
and lowest summer operation cost, but higher winter operation cost.

Water Furnace has an excellent reputation. I don't know the other
brand.

Get a load calculation done. See if your power has a rebate program.
They might do the load calculation free, ours does.

Stretch