A lot of it depends on how you design the system. Using the ground as a heat source requires a relatively large installation as you need to make it big enough

A lot of it depends on how you design the system. Using the ground as a heat source requires a relatively large installation as you need to make it big enough to draw heat from a large area, even as you use it year after year. However, you can also use the ground as heat storage, and pump back heat during the summer. This greatly reduces the size, as you are not at risk of "exhausting" it.