As you can see from the above replies, there is no one answer. You also need to take into account the sound signature that you want (bass-focused, mid-focused, mid-recessed (U or V shape), or treble-focused; there are more). I personally lean towards a flat frequency response (FR) for my speakers and headphones; so much so that I purchased the SoundMAGIC HP100 (closed back, flat FR) over the SoundMAGIC HP200 (open back, bass-focused FR). You could also be as objective or subjective about you experience as you want.
