What is the most important component in your system.

Everything should be at the same level of quality or it is a waste of resources. (Having something not able to be as good as it can since other stuff is clouding the music) So I say the Synergy of the whole system is the most important.     
This ties in with knowing or being able to discover what component(s) is (are) ’holding back’ the rest of the system. In the past few months I upgraded my speakers and DAC.   For me, right now it is powercords.   MY last purchases of powercords were over six maybe seven years ago. So I bought a few new upgraded ones of my favorite brand, and wow yeah, they have improved. So I am buying a bunch of new ones.And I was surprised how much of an improvement from one step up better PC could be on just one place...On my setup(But tiny variations are always noticeable to AUDIOPHILES!!!)

@elizabeth .... Nice response.....And i agree whole heart.... Also its very interesting to see what everyone else thinks and says.

I just rediscovered the joy of a well recorded SACD. That, leads me to believes that once the whole system is dialed in, that "single" component belief is made irrelevant. 

It's now down to the source. There are still gems hidden in those pits and grooves, if recorded correctly.

All the best,
Nonoise

The one I just bought 

I think that for me the most important thing isn't a physical component, but the mental experience gathered over the years through experience that helps you to blend the separate parts together with some kind of skill as well as a little intuition to get a good result.