I had an Olympic arms version of the M-4. It had a bull barrell, and for a 5.56 round was exceptionally accurate up to 300+ yards. I'm not that great of a shooter either. With a better shooter who could account for windage, the accuracy could have been much better at a farther distance.
Olympic arms makes a quality rifle, and the bonus for me is that their manufacturing plant is only a couple of miles from home. Upgrades were able to be bought through the sales shop at the manufacturing facility, and were 5% above wholesale.
If there were ever any problems with it (which there never were) it was a quick trip right down the road to have it serviced.
For someone who doesn't live close, it would still be a great buy. It's quality is great, as well as their customer service. They are very reasonably priced also, in comparison to a Bushmaster, Armalite or Colt.
http://www.olyarms.com/
Just my 2¢