To name a favorite Bryston amp is a tough call, indeed.
I do like the 2B-LP for its simplicity and its 1U form factor.
I love the 14B for its sheer endless power and its finesse at low levels.
From an engineering standpoint, I like the multichannel amps, namely the 9B and the 6B, best. With the 9B ST a new and improved signal routing and grounding took place which distinguished this amp from the previous ST amps. And if you take a 6B SST into your hands you literally feel its compact power. The top cover of the modules looks even more precious as it is not the usual metal sheet used on the other Bryston amps. The additional care taken on the 6B amps is one reason why a 6B, being more or less a 3 channel version of the 4B, costs more than 50% more than a 4B. The only thing Bryston missed on the 6B is that they moved the power module to the other side of the amp's chassis, compared to the 9B (looking from the back, it's located on the left for the 9B and on the right for the 6B). This way, the heat sink of one channel is on the very left side of the amp's chassis when seen from the back. When rack mounting the amp, some racks offer brackets where one can put the equipment on, supporting the equipment chassis on the left and the right side, taking torque from the front panel. Those supporting brackets would, however, cover the leftmost channel's heat sink completely and therefore cannot be used with a 6B.
This, however, did not prevent me from voting for the 6B 3-channel amp as my favourite Bryston amp, for its sound and its look and feel, especially with the black 19" PRO front panel.

Cheers!
Markus