We have stayed in each. We ended up in an A because our B suite had no working outlets and they upgraded us after a day in the B suite. I was really disappointed when I saw the B suite compared with the C. It was not worth the extra money. However, we were delighted with the A for the cost of the B.
The B cabins are almost the same as a C cabin. The configuration of both of these cabins is essentially the same. The C cabin has a loveseat and the B cabin has a couch. The difference in the size of the cabins is the diffence in length of a couch versus a loveseat. Otherwise, the interior is exactly the same. The balcony, too, is a tad bit larger, but not very large. For the money between a B and C cabin, I would never again choose a B over a C. The value just isn't there. The difference in the other cabins beneath a C is that they either have a window or porthole and no balcony.
When I first saw the B cabin, I was very disappointed compared with what we got on the Mariner and Voyager for the same money.
The difference between the B cabin and an A cabin is entirely different. If I had the money, the A cabin is the way to go if space is important to you. The configuration of this cabin is very different. It is one very large, wood panelled room. It has a large desk and bar area and is elegantly appointed. There is no curtain to separate the bedroom from the sitting area. It is a lovely size. The bathroom is the same as in all the cabins, but the deck is very long and much larger....like the penthouse suite balconies on the Mariner. Being that is was Tahiti and we had floats and wetsuits and spent a great deal of time outside, we loved having the extra balcony space. It made for a very comfortable time on the ship.
That being said, it was much more expensive than the B suite. So, my advice? Skip the B suite and choose either the C or A suite. The C suite comes with jewelry (just kidding. but think what you could buy with the savings)!