Just to chip in, I'd note that you can't compare two map types of completely different purposes.Frankly, one or the other is just not right.
Terrained has the purpose of terraforming and using an actual terrain to build on, instead of making one yourself, which, most of the time, takes up most of the build time.
When a private flatland would be a solution to wipes, where Guest maps could be wiped on a weekly basis, with the Builder map having more room to build etc.
Comparing them would just not be right.