I've shot, cleaned and handled both rifles, and I'd prefer the AR-10 for your purposes. Unless you're planning to shoot/plink targets 400-500 yards away, an AR-10 will be the best platform for a scope and bipod. There are plenty accessories to modify the gun with from Armalite.
If you really want a M1A, look into the new M25 Carlos Hathcock edition. It has a built in pictinny rail on the receiver, and the receiver itself is lugged so it can be braced rigidly in the stock. Gets 0.75 MOA out to 300 yards according to some reviews I've read. Problem is, it's $3000. However, it's the ultimate rugged semi-auto sniper rifle. The Scout model isn't bad either, but you'd have to use a "scout" style 2-3x powered scope on the front rail. It works great out to 300 yards.
Anyway, for the money, I'd go with an AR-10.