Washington D.C

I don't do hop-on/hop-off buses, and certainly not in my hometown, so I can't help you much. I'd check each company's website in hopes of finding a map showing the stops. At one time I think Tourmobile had better access at some of the monuments on Park Service land (Lincoln, Vietnam, Korean, Jefferson, FDR), but that may no longer be the case. And the only ones that matter are the ones you're interested in. I think you'll have to do some walking at the sites I listed. If it's any comfort, the people using Metro have to walk a lot farther. You didn't ask, but I find the FDR and Korean Memorials the most visually interesting.

I'd also check TripAdvisor for ratings and reviews. It's possible that bus frequency varies. I'm not sure that standing at a bus stop, waiting on a bus, is much more pleasant than walking. Especially if your trip is in the summer.

The Circulator is much cheaper than the other systems - it's about $1-2 per ride. There are multiple routes but the really touristy one goes along the Mall museums. I wouldn't attempt to photograph from this bus, as there is no open seating up top. It functions as a regular bus where you have to pay a fixed fare per use.

The other two systems are your typical hop-on, hop-off buses...more expensive but allow for getting off at whatever stops you'd like.

We lived for several years in the DC area. You mentioned the D word, "driving." Be aware that if you are going to DC on a work day that the rush hour starts at 5AM and ends about 7:20PM. Traffic is awful. Union station may be a good solution, although taking the METRO is another option.

The DC sites near Union Station are very walkable. The Capitol building, Supreme Court and Library of Congress are close, then the Mall, with all the wonderful museums. Closer down to the White House are the Archives building, Ford Theater then the Washington Monument, continuing on to the Lincoln Memorial with the Vietnam Veterans and Korean War Memorials as well as the FDR and WWII Memorial. The Jefferson Memorial is a bit out of the way.

Also, close to the Mall is the Bureau of Printing and Engraving.

You can use Google Maps to tell you the walking distance and estimated walking time (sounds like you'll need to bump that up a bit) between any two sights.

If you take the Circulator, I'd look at the route map and see where you want to go. You may not need to travel all the way into Union Station and may find that a garage (but check how late they're open--many in the business core close at 7pm) in another part of the District will suit your needs and/or be closer to the Circulator routes near the Mall.

As Agnes mentioned, the Circulator is a fixed-route traditional transit bus and does not provide the open-air or narration some of the other buses have.

Have a good time! And if you're coming in August during Congressional recess, the good thing is that traffic is usually much calmer and lighter.

Some friends came to visit me last year and they were very disappointed with the circulator. They said the commercial companies seemed to come by much more frequently and they felt that they spent a lot of time waiting for the bus. There is a huge difference in price, so only you can determine if you'd rather spend extra time waiting to save a lot of money.

I regularly drive down Independence Ave. and I see the Old Town Trolley more often than the Big Red bus (or rather the Old Town Trolley seems to more frequently cut in front of me and it is big and awkwardly shaped so one notices it when one is in a small car). I think it would probably have good views for photos as the seats are fairly high up and windows are large.

Regarding parking, pay close attention to parking restrictions if you park on the street. Tow trucks are always out in force during rush hour. Garage parking can range between $15 and $25 a day.