a bs or a fs....would depend on your room size, preference, and type of music.
among these, it is the "preference" thing that gets changed as your experience and exposure to audio goes through time.
normally your standard and criteria would get more and more critical as you listen to many a different good 2ch systems.
train your ears. know what's important and what's not important as far as your personal criteria for good sound is concernd.
there are no shortcuts. just take your time to listen, enjoy, ask around, read...