Whoever was in charge of procuring the first batch of M16's was an idiot. Who cares what happened in Vietnam, apparently we were stupider then.
Today we know what works and what deosn't. Yes, the RRA's are better than the OG m16's, but that deosn't mean that there aren't way better rifles for the same cash expense in todays market. For those that like Shrubby, Cerberus, Del-ton, hey more power to ya', but when someone asks for a recommendation, I'm going to bash those every time.
1911crazy, you wanted advice, I say skip both. Look towards Colt, BCM, LMT, DD.
Similar cost, better stuff.
Look at BCM's epic list of upper recievers. Let us know what types of uppers may work for you. BCM has an example of just about every type of upper you could want. It'll help you get an idea of what type of carbine setups are available. Also look at one of Ar15.coms pic threads. Let us know what type of style you like and we can figure out the best matching deal.
Epic Ar pic thread to give you some ideas:
http://www.ar15.com/forums/t_3_118/510264_Official_AR15_com_Picture_Thread_part_22.html
BCM's list of majik uppers:
http://www.bravocompanyusa.com/AR15-Upper-Receiver-Groups-s/1.htm
As you can see there are a great many types of Ar styles out there. Short range carbines, to longer range SPR's, and everything in between.