Generally speaking and based on discussions of this subject in the past on this forum, the 7bs will sound slightly better. However, if space is an issue and a single unit for an amplifier is preferrable to two units, the 14b is a better choice. The price difference between the two models is not an issue because you'll spend less on speaker cables for the 7bs. The cables for 7bs can be much shorter since each amp can be placed next to each speaker. I chose the 7bs for my all-Bryston system. I could have gone with the 4b for my speakers (B&W 803D) but knew the upgrade bug would eventually strike if I did. With the 7bs, there is no upgrade bug. They sound great.
Hope this helps.