I've shot ARs for over 10 years, taken them to DCM competitions. First of all, if you do any competitive shooting, a standard 20" barrel is mandatory. That being said, there is no theoretical accuracy difference based on barrel length. That being said, a longer barrel is always more accurate, because you have a greater sight radius, more mass etc. (HUMAN FACTORS) Also, for follow-up shots, they don't heat up as much as short bbls., which changes the dynamics of the bbl. Then their is rifling twist rates, stainless barrels, fluted barrels, free floated barrels and we can continue on forever. The bottom line is, what do you want to do with it? Then you can start filling in the blanks. Cost is also a consideration.
