If your talking about Service Rifle Class for NRA High Power matches, the only .223 Rem that qualifies is the AR-15/M-16. Service rifle has to be a rifle that has been issued to the military. The common ones are AR-15/M-16, M1A/M14, M1 Garand, 1903/A3 Springfield, and the occassional M1 Carbine and 1917 Enfield. Everyone except the AR-15 is a .30 caliber of some sort.
For a factory gun the very best for the money is the Rock River Arms NM A2 or A4 model. If you go the custom route or factory tuned route, White Oak Precision seems to be the best their is. I just recently bought a Rock River Arms NM A2 and love it. Hope this helps.