ETA: Stay away from the carbon models. It was an answer to a question nobody asked.
Now wait a minute, either my weather alarm is sounding, or my BS detector is going off.
For those that missed the memo, there's one thing 'tactical' rifle shooters are always asking for: A lighter weight rifle.
That was the whole point behind the M16/AR-15, if you'll recall.
Carbon composite, like in the Bushmaster Carbon-15s, is much lighter than Aluminum.
The Carbon composite rifles have yet to undergo enough testing and use for me to trust them. Thus I won't be getting a carbon rifle for a while. But so far there haven't been many serious issues with it, the biggest problem has been jamming while chambering a round, but from what I hear Bushmaster worked that out. If, in a years time, no serious issues have come forward, you'll see me picking one of those up and making a SHTF lightweight carbine out of it.
But the Carbon rifles are
an answer to a question lots of us have always asked: "How do we make this rifle lighter?".
However, with reference to the topic at hand: I wouldn't suggest a carbon rifle for a first-time AR owner. Go with the traditional aluminum rifle, from Bushmaster, Rock River Arms or Armalite. Stay away from Colts, they'll give you warts [
]. I'd go with either a standard 20" A2 or a 16" mid-length A3/A4, if it's your first rifle.