You are really comparing an apple to an orange. They are based on totally different systems. I would suggest you just go to a range. shoot one of each, and pick the one you like. In general, the M-1A is somewhat more reliable, with far less maintenance, than the AR variants, but is heavier to carry. You are either a 1950s "wood and steel battle rifle" guy, or a 1960s "plastic and aluminum battle rifle guy." At the ranges you are talking about, assuming use of the same ammo, there is not going to be any real difference in the effectiveness or accuracy between the two rifles. Just see which one handles best for you.
Regards,
Mannyrcok