The small group tour is great. We were able to talk with the driver and get more information. The driver was great! He was very friendly and was flexible with time at the various stops.
This type of tour, a small bus, is the way to go. We never have been able to see the monuments without spending hours of walking. After the tour we decided what monuments to go back and see more of.
If you have a short stay I recommended the short bus tour and using this company.
Buying tickets was easy. I strongly encourage buying tickets in advance when DC will be busy, e.g. Cherry Blossom festival, summer months, etc.