which is more accurate, more reilable, and just plain out better. it seems the more modern AR10 would be more accurate, but considering how often AR's have trouble id guess the M1A is more reilable. I think both use the same Mag in .308. is the AR10 in .243 probably better than the .308 version?

I wouldnt want it in .243 i would want a battle weapon in a battle caliber aka the 7.62mm/5.56mm.

Ok i dont own a AR10 so i cant really comment i do own an AR15 and a M1A however.

My feelings toward the M1A are it is a wonderful weapon if your gonna use the iron sights on it,and they are without a doubt the best iron sights i have seen on any weapon with practice you should be able to hit out to 500 yards with it.
I wanted to do the scoping it out thing with M1A however it is just not the best platform for that.
The AR10 as far as a platform to scope it out and make a MOUT Monster out of it,or make a tactical rifle it is your best bet.
But if you want a tough battle rifle with exellent open sights that is a very reliable weapon then the M1A might be a weapon to look at.
But im not gonna tell you which weapon is better because some people like M1A's and some like AR10's others like FAL's.If you put any of these rifles in the hands of a man who knows how to use it well and watch out its not the weapon its the man behind it.

I've got a AR10A4 with S.S. barrel and a preban standard M1A.This is like asking which of your kids do you like better.Accuracy--the AR10 wins by a red cun* hair.They are both fine accurate weapons.The AR10 is a better optics platform.Reliability--the M1A.Ease of cleaning--the AR10 hands down.Cool factor--the AR10 looks like it's on steroids but the retro look of a walnut stock M1A is cool too.If I ABSOLUTELY had to make a choice it would be the AR10.But if you ask me tomorrow I might say the M1A.They are both fine weapons.

which is more accurate,
my AR-10A4 is a .75 MOA rifle
My M1A National Match is also .75 MOA.
a standard M1A is a 1-1.5 MOA rifle.

the M1A is far more reliable.  but if you keep it clean and oily and keep the dust cover closed the AR-10 will run like a top.

it's the same mag with modifications to function in the AR10.

when you chamber and M1A it has a sound that is sexier than racking an 870 pump shotgun.  when you hear that particular noise you know immediately something is about to die.  the AR-10 makes a gravely sand paper sound that has never given me goose bumps.  

but the AR-10 can be modified with all sorts of custom parts to personally fit you!  so you can buy both guns for 1200. and another 100-200 in parts for the AR-10 and have a custom fitted target rifle.  with the M1A what you bought is what you got.  outside of a rubber butt plate ARMS mount and a cheesy nylon cheek piece you can't modify it much unless you are willing to drop 300.00 for a McMillan tactical stock with Adjustable cheek piece and extra trimming.    

what do you want to do with the .243 that you can't do with the .308?  the only thing i can think of is prairie dog hunting.