The blockier the better (to a point).
I intentionally produced a blobbier print because it held better in the ground
10% infil works and has decent strength but if you intend to pound on it go higher
In general printing the stake on its flat works better than printing it laying down (less support material is needed). This does compromise some strength however
Please take care in handling the completed parts as the edges, especially those around the top and the hole, and the tip can be quite sharp. It is too easy to cut yourself while trying to push in the stake
Clean out the hole, and optionally shove a nail through it and bend it to create a hook