On HAL, location is the only difference. BB cabins are the front few 4-6 cabins and the back few 6-8 cabins almost always on the same level. B cabins are in between and are considered better because they are closer to stairs, elevators etc. This is open to debate however, since they BB cabins are a bit "out of the way, traffic and noise is less. Many people prefer the BB for this reason and actually prefer being at one end of the ship or the other because of the views.
The ships might vary but this gives you a general idea. What ship are you booked on? We're on the Veendam, 1/17 in a BB cabin.