You're looking at a lot of potential maintenance down the road with a pump and dump system. I think the closed loop system with the exchanger coils sunk in the pond is by far the better and less expensive choice.
Sure there may be a filter to clean (my geo guy says that this is not too often). The closed loop is not as efficient, has its own concern that it could get buried in the pond, and has more up front cost involved (not as much as burying the loops but still more cost). Plus... I don't know whether a pond is feasible without a pump/dump from the geo unit.
What maintenance are you speaking of?
