This is a tough question to answer. Let's look first at whether to go open loop or closed loop. Open loop systems are best applied in situations where the house is, or will be, served by its own water well. A slightly larger well pump is installed to provide for the water required by the heat pump. A major consideration is the disposal of the water.
Water quality is also an important issue.
If the water is of good quality and the house is to be served by a well for domestic water, serious consideration should be given to the open loop approach. See the costs section of this report for capital costs for the open loop system. If the system is to be a closed loop design, the choice between vertical and horizontal system is sometimes a difficult one to grapple with. The major advantage of the vertical design is that it places the loop in a much more thermally stable zone. Soil at 100 ft is not subject to the same temperature fluctuations as soil at a 4 or 5 ft depth.