Auto biasing is more convenient than manual biasing. That's a good thing. Is there a sound difference? Each person will tell you something else. If you are going to put the amp inside a rack, you may want to put more emphasis on autobiasing but if the amp(s) is(are) open, it doesn't matter.
My experience with a BAT (auto) and both Manley(manual) and Atma-Sphere(manual, but better executed) affirmed my opinion that manually biasing an amp can be a pain in the ass but really doesn't make a difference. One byproduct of owning a Auto biasing amp was that I never wondered if the amp would sound better if I rebiased it. I trusted that it was always at its premium setting.
My current amp is the Atma-Sphere which is biased with a different method than most amps. Still manual but IMO more efficient.
Others with more time and tube knowledge than myself will surely flame me and tell you how wrong I am, but you asked for many responses.
My experience with a BAT (auto) and both Manley(manual) and Atma-Sphere(manual, but better executed) affirmed my opinion that manually biasing an amp can be a pain in the ass but really doesn't make a difference. One byproduct of owning a Auto biasing amp was that I never wondered if the amp would sound better if I rebiased it. I trusted that it was always at its premium setting.
My current amp is the Atma-Sphere which is biased with a different method than most amps. Still manual but IMO more efficient.
Others with more time and tube knowledge than myself will surely flame me and tell you how wrong I am, but you asked for many responses.