It was really handy to be able to hop on and hop off the buses, however to be able to really benefit from seeing all the sights, you need to be sitting on the top deck of the bus and this wasn't always possible when you tried to get on part way through the tour. If you want the proper experience, do the whole tour(s) and then use the bus as a taxi service for the rest of the time. The guides are great, very informative and very funny, remember to carry some money to tip them, as they get by mainly on tips. The attraction passes were very simple to cash in and well worth getting, as they save you a lot of money (and a lot of queuing at times as well!).
Hop-on hop-off tour was operated by the tour company. The first ride we took was the best. Our tour guide was awsome and really funny. The other guides were pretty boring. Buses weren't in best condition either. There was a leak, so when it rained, water was dropping on me. Sometimes it was difficult to find the bus stop. They are not marked very well plus there are other bus companies which can make it even more confusing.
Attraction pass worked great. We could have decided on witch attraction we will go when we wanted (it wasn't necessary to decide at the beginning when we received our tickets). I think it was good value for the money (we have chosen Top of the Rock at Rockefeller Center, Empire State Building and night boat ride alongside the Manhattan and Statue of Liberty - I recommend all three of these).
Booked the red your buses before our trip, with 5 attractions to do in 3 days. They are a great way to find your feet in the city if it's your first time in NYC, we were up and out on the first morning arriving at the tour company centre to pick up our tickets just after 7:30am, no queuing, no problems. Overall great value and saved time and money.
Tips - if you get on a bus with a miserable guide, hop off at the first chance and get on the next bus, they are only about 10 mins apart, some of the guides are really good and very funny, unfortunately some are not very good at all, its worth the extra 10 minutes wait to get a good guide.
When you hop-off, take a minute to look around where you've been dropped off so you know where to wait to get on the bus when you are ready or they will go whizzing by....
All the attraction tickets are exchangeable at the attractions themselves (wave your tickets at staff and ask which queue to join), the exception for us was the statue of liberty ferry! eventually found 2 tour company guys sitting on a wall in front of the big black building at the other side of battery park that exchanged the tickets (you'll know what this means when you get there.....)
Make sure you have plenty of dollar bills, you'll be expected to tip for everything while you are there including each time you get off a bus.....
Above all be an early bird, the attraction queues do get very big by mid morning!