Most of the shooters I compete with including myself go the custom route. White Oak Armament is the predominant custom builder of uppers used around here N.E., there are others Compass Lake Engineering, Northern Competition, First Strike, Accuracy Speaks to name a few that do top shelf work. Most of the lower work, which is usually putting a new trigger in is fairly easy if you're handy. That's my advice, buy an upper, a complete lower and change the trigger unless you like what it has, add weight to suit and go shoot. RRA's and Bushmaster DCM's are good rifles though, I've seen some great scores shot with them. It comes down to money, you may spend a couple hundred more going custom but you'll have exactly what you want and have a competitive rifle with a quality barrel and a gunsmith that will support you if there's a problem.