Like SD, I am an unapologetic fan of Bryston. In fact, I run the 4BST and 5BST in my HT arrangement. Have listened to the 9B any number of times and think, quite simply, you can't miss if that's the one you settle for. Superb piece. It's what I would have bought had I not already owned the 4B, which I am unwilling to part with. SD's right: Bryston amps are very conservatively rated and behave as though they are a lot more powerful than published specs.
Figure out those things most important to you and let them drive your decision: sound, quality of construction, warranty, your tendency to buy the latest and greatest toys, what have you. If you like to settle on something for the long pull, you'll have to look long and hard to find something other than Bryston to fill that bill better. For some people it's Krell, others, CJ, Levinson, McIntosh, Pass. All great stuff.
The equipment from the folks at Bryston does just fine for me. OTOH, if you're a compulsive upgrader, buy whatever suits your fancy. I don't have the budget for that indulgence, but salute anyone who does.