The Big Bus hop on hop off tour is phenomenal! I cannot praise these guys and girls enough. They are very enthusiastic about the tour, and they give you lots of time to ask questions about different things you are seeing. My girlfriend and I did all 5 tours; Uptown, Downtown, Harlem, Brooklyn and NYC Night Tour. They are very informative and exceptional.
A piece of advice, if you have a fear of heights, let your tour guide know on the Brooklyn tour. The Manhattan bridge is very high up and may cause some panic.
Only complaint about Big Bus is the Brooklyn tour. "Little Boy" as he asked us to refer to him by was an incredible guide. 10/10, enthusiastic, funny and answered every question posed to him. However, my girlfriend and I wanted to wander around Brooklyn, but with only 2 stops, and the infrequent buses, and lack of depth into the borough, it did not seem very worthwhile. I think it would add a lot of depth to the tour, and make it more fun for the guests!