He just wanted to know which spec is performing best on every boss, and since i couldn't be able to find anything about this i decided to ask
At the moment Demonology performs well on every single BRF fight. Affliction and Destruction can catch up with the right gear on specific bosses, but Demonology is the go-to spec.
Guide to talents per boss here, as well as some fight specific tips.
Thank you everyone!