Cherry Hill without a doubt. There are a few cheaper alternatives,: Little Bennet,Pohick Bay,Bull Run, Prince William Forest, Adventure bound DC, However none opf the alternatives are quite as nice or quite as accommodating to tourist as Cherry Hill.
The alternatives are all decent places that I have been to, But they just are not as tourist friendly as Cherry Hill.
If you are already familiar with the DC area, the alternatives may work.
But if you are not familiar with the area stick with Cherry Hill.