I recently upgraded from the 4B ST to the MC352 - each amp is the immediate predecessor of the ones you are considering. While the Bryston is no slouch (I was happy with it for 5 years), I find that the Mac sounds less like audio, and more like live music. I'm definately listening to my system more since I upgraded.
While the Mac warranty is decent (3 years), nothing compares with Bryston's 20 year warranty. On the other hand, Macs are very cool running and long lived amps - there are lots of 20+ year old Mac amps still in service. And if you do need a repair, there are plenty of places that specialize in old Mac gear, and lot of parts are still available from the factory for vintage Mac gear.