Steinway
Steinway Model A vs Model B
Between the A and the B you are choosing how much grand your room can take.
The difference
The Model A is 6 feet 2, the Model B just under 7 feet. The B has noticeably more power, depth and projection. The A gives much of the Steinway character in a piano that fits a normal music room more easily.
Which to buy
If you have the room and want the fuller sound, the B is the more complete instrument, and the more sought-after on the used market. If your room is normal-sized, the A is the sweet spot, more piano than the M and O without needing a B-sized space. Measure your room first, then choose. If the budget is the issue, a reconditioned Yamaha C-series grand covers this size range for far less.