Washington DC

Take the double decker bus tour. $45 per person and worth every penny

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.

Cherry Hill..without a doubt

We considered Bull Run but ended up at Pohick Bay Regional Park. More woodsy and half the cost of Cherry Hill if all you need is electricity. We took the Yellow Line from Huntington station to get downtown. Pohick is also convenient to Mt. Vernon.

First choice would be Cherry Hill Park, has every amenity you can think of plus location to DC.

Slightly off the radar would be Bull Run Regional Park. Campground is about 15 miles from the Vienna Metro Center Station. Campground is more rustic but still has all the basic amenities.

Mike

x3 on Cherry Hill. Went there last summer and it worked out great. As said bus pick up and drop off right in the park to take you to the trains to get in and out of DC. Once into DC the subway pretty much takes you to many points throughout the city. Enjoy.

Cherry Hill.

The best is Cherry Hill park. Metro bus picks up at the park and takes you to the train.