Love em both, but here goes…
If both are fed properly and cared for half way decently, I don’t think one version is any better or worse than the other.
We will start with the what’s. M1A is a copyrighted name for the M14. In this discussion, a M1 is a M1 Garand, not a M1 carbine. That is a totally different beast and doesn’t begin to compare.
So we will go with both options being newly manufactured by Springfield Armory, the corporation in Illinois. Quality being the same, I would go with the M14, I mean the M1A. Only because the deficiencies, as minor as they are, were corrected, these break down to the gas system and ‘clip’. On the Garand (M1) the operating rod is one unit. On the M1A (M14) the operating rod is separate from the gas piston. I’m sure that this must be better, even if I don’t see it right off. Oh, yea, the gas is metered. But if I feed the weapon correctly, what difference does it make. And the big difference, the detachable magazine. I will go along with the magazine over the 8 round en-block clip, except when shooting prone or from a bench. Hum. So, we have the different chambering. The 7.62X63 is not as prevalent for reloading as the 7.62X52, that’s the brass only, everything else is the same. As I reload and 7.62 NATO is spewed by lots of military full automatics, surplus brass is easier to get. The target or game won’t know the difference.
The purist would never drill and tap a classic Korean IHC. Well, I wouldn’t. The M1A has a provision for mounting a scope.
Does this indicate that one is more accurate than the other? No, ammunition variables and how each weapon meshes with the different loadings make more difference in accuracy than the weapon.
Stop, one weapon will ‘like’ one type of ammunition better than another and your pet M? may shoot one hole at a thousand yards, where that other M? just can’t do it. For me, I can’t shoot one hole at a hundred yards with either my M14 or my M1. No matter the version, are you going to stress your weapon unduly? Feed it right and it will work for you for a long, long time.
If you want to work for the ultimate accuracy, get a bolt weapon. If you want the flattest trajectory and greatest velocity and most energy, get a bolt weapon. If you want a small piece of history and a magnificent Battle Rifle, get a M1 or M14 (M1A) or both.
Moving on, if you are looking at second/third/fourth/more-hand weapon, that weapon could be anything from a re-weld de-milled M1 to a copy of a M14 made by who knows. I will not go there. Just too may variables to consider here, collectors value, wear and abuse, major cost differences and on and on.
We must remember these things:
Both are ‘Battle Rifles’ for war. In a battle, hitting your enemy any place from the chin to crotch at 100 meters is fine. Yes we want better but that is what was needed.
Both the ’06 and the 308 will get the job done and well.
For hunting, both have a long history of taking big game.
The 30.06 has been the standard that everything is compared to for as long as I can remember and that’s been a while.
Which is best? The one that you have. Sorry, I can’t give you a definitive answer. My advice, get one now and save up and get the other one latter.