We took a hop-on hop-off bus. The tour was informative, but the seat are made for midgets. When you get on, look around for seats that have good leg (knee) room.
We were taken around town by friends. Make sure that you have a chance to visit the wall separating the Catholic & Protestant districts to see the murals.
Typical bus tour of a city. It would be ideal to get the first glance from the bus and then come back to see certain attractions in depth, but there is not usually enough time to do that.