Coming to Washington next week and plan to see all the monuments and sights. What is the best "hop on/off" tour in Washington? There seems to be a bunch of them: Old Town Trolley, Lil' Red Trolley, Tourmobile" etc. Is any one more desirable than the others? We have the city Visitor's Guide and have done some research in the internet- of course, each company says it's the best service- just wondered if anyone has an opinion.