I slightly prefer the Garand for shooting prone, because I can get a lower, more stable prone position without the magazine in the way. The Garand is harder to load prone rapid fire, but the prone match is usually slow fire. If you have a single load device {SLED}that works well, the loading is a wash.
I slightly prefer the M1A for standing because I can use the magazine as a palm rest. For the other positions there is little difference.
I have not used either in combat, though I did use a DRMO surplus M14 for SWAT for 3 years or so. I didn't shoot at anyone with it, the M14s went to the drill team for parades and funerals and we got new AR15s. If you had all your 30-06 in 8 clips you could keep up a pretty steady rate of fire I suppose. The darned clips are so expensive they aren't really disposable any more. Domestic shootouts are usually settled in the first few minutes anyway.
I think on the whole I find bedded M1as with a good barrel slightly more accurate than a comparable Garand. A good Garand will run rings around a fairly average M1A. All the above will hold the 10 ring if you do your part.
