Well I noticed a whole bunch of "which is the best AR", "I'm building a AR what to use" threads. While I know there is much to debate on which brand is better then the other. I would like to know what part on the AR has the most effect on accuracy and reliability? Lower assembly, upper assembly, barrel? What would the great minds of THR.org say has the greatest affect on the overall performance of an AR-15, or perhaps a list of greatest to least effect.