No matter what type of HVAC system you choose for your new home, the better the exterior is insulated, the more efficient your system will be. A geothermal heat pump is very efficient, but the proper R-value and tightness of your home will lower utility bills and increase the life expectancy of your system. Basically, good insulation lessens the workload. The conditioned air produced is better retained and unconditioned outside air has a harder time infiltrating your home.
A very tight and well-insulated home does require some added consideration. The exact type and R-value being installed needs to be relayed to your geothermal installer. This information is critical in determining the proper size of your HVAC equipment. An incorrectly sized unit can lead to all kinds of problems, no matter how well you have insulated.
Also, a very tight home needs to have fresh outside-air introduced into the living environment to maintain healthy indoor-air quality. A good contractor will recommend one of the many methods to do this, from a simple fresh-air skuttle to a heat-recovery ventilator.
The bottom line — if your home has great insulation, your geo system will produce even lower utility costs and generally last longer. Back to the analogy, definitely go with the chocolate sauce and sprinkles!