We used Toumobile once. We found it a mixed bag. You'd get on and have a great, fun, informative guide . . . Then the next bus'd be led by a lackluster guide. If you don't like the first one, don't worry -- it doesn't mean you're in for a bad day. The best guide we encountered was a young guy, a college student, who'd made his spell into a game show format. He certainly held my kid's attention.
We've also done Monuments by Moonlight. It's also a fun experience, but more focused, and the time is shorter. I wouldn't do both on the same trip . . . Too similar. I think I liked the moonlight better.
The bus is a good choice for seeing the monuments. They are very spread out, especially Jefferson's. Check Google maps and the metro map to see whether you'd be good with walking that far. The metro travels mostly to office buildings. If you're going to the monuments, you're going to get off the metro at the Smithsonian, which will put you near the Washington monument . . . And you won't be near another metro station.
Don't plan your bus tour day for the same day you plan to visit the museums.
We did not ride the Circular bus. They're the on who run the anti-Christian ads on the side of the bus, and we just can't do it.
Consider visiting the old post office (it's a national park). The view is better than the Washington monument, and no lines.
Skip Ford's Theater. I don't know how they make something as interesting as Lincoln's assassination so dull.
Everything in the Smithsonian complex is worth seeing, but I like the American History museum best.
Don't miss the Holocaust museum. It isn't part of the Smithsonian.
You can see a free show every night at 6 or 6:30 at the Kennedy Center. Might be good, might not be good . . . But the Kennedy Center is worth the trip. The metro doesn't go there either.
Try Union Station for affordable food.
I like to walk, so worked out for me.
