Re: Which M1A?
The Springfiled offerings are the best "bang for the buck" currently. With the lifetime warranty--which follows the gun and not the original owner--it's hard to beat 'em. Now if you're looking for a rock solid rifle that will perform, take your time and source all USGI components for as much of the rifle as you can. This route will be more expensive, but if you plan to hold on to the rifle for years, it will be worth it. The only USGI part that cannot be had is the receiver. I would reccomend a Criterion barrel for the cost savings compared to something like a Krieger or Obermeyer.
The Springfield receivers are decent. The ones in serial numbers below about 100,000 tend to be more "in spec" than the current ones. This is truly apparent if you plan to mount optics as the scope mount integrity for most offerings is dependent upon the receiver being perfectly in spec. The Polytech receivers are very nice, and generally are known to be in spec--more so than most newer Springfield receivers. The Polytech receivers are forged, which is a big plus. The Sprinfields are cast steel.
I would advise you shy away from a complete Polytech rifle as the barrels tend to stretch after many rounds which leads to your headspace going out of spec. A Polytech receiver, built with all USGI parts in serviceable condition with a Criterion barrel will give you many, many years of solid service. If it was my first M1A, and I had it to do over, this is probably the route I would take. But, if you're like me and don't want to wait for the parts to pop up and wait for a competent builder to assemble your rifle (usually takes many months for the reputable guys like Ted Brown, SEI, Art Luppino, Ol Hook Boutin, etc), then plop your money down on a used Springfield M1A in excellent condition and shoot it till the barrel is toast!