I hope the AR-308 will be more accurate since I'm taking delivery of one very soon. Once I shoot it I will post the results. I ordered a Rock River 308 with a 26" varmint barrel a year ago and I hope to get it in the next few weeks.
I have read many post on websites such as Sniperhide.com and they almost all say the AR platform is more accurate. The M1A definately scores high in style points but from what I gather, 1-2 MOA is the norm on most models. I also hear they take quite a bit of tuning to make them consistant in this range. I love my M1A NM but its just for casual range fun. If I wanted to get serious, an AR 10 would be the way to go.