I have two questions. Other than the Sig P210, what is the most accurate 9mm semi auto pistol from a rest at 25+ yards that is currently out on the market to buy?
Second question. What is the most accurate polymer pistol (limited to 9mm or 45) at 25+ yards from a rest that is currently on the market for sale?
Probably an X-Five or X-Six for current-production 9mm pistols. Actually, probably one of the top semi-custom 1911s with an accuracy guarantee in 9mm, like BAC said, but I can't speak from personal experience there, as I've never shot one of those in 9mm (and would never buy a 9mm 1911). (Regarding the P210, be aware that the current-production German P210, while a superb gun, is definitely not built to the same standards as its Swiss forbears and is not capable of the same level of accuracy.)
As for poly pistols in either 9mm or .45, not sure, but the comically hulking HK Mark 23 is probably as good as any. Or perhaps one of STI's hybrid-frame 2011 pistols.
Can someone tell me the difference between an x5 L1 and the current newer x5s? Is one more accurate than the other?
The newer ones have an ugly rail and fairly unattractive overall "restyling" (my opinion, of course), and I've heard rumors that they have a greater number of MIM parts (not certain about that), but I don't think there's an accuracy difference. The newer ones do have the advantage of being a bit less expensive on average, from what I've seen.
At some point in 2015, however, all Sig production will move to the U.S., and I've seen nothing from Exeter/Newington to give me any confidence whatsoever that they are capable of building X-Fives, X-Sixes, and P210s (the very thought of these is just laughable to me, especially the idea of an American P210) to something resembling the standards of the German Mastershop. If you want one of these, buy it sooner rather than later.
The pistol with the best accuracy-to-dollars ratio -- this is obviously conjecture, as no standardized testing exists -- might be the new Wilson Combat Beretta 92G. Bill Wilson is shooting 6-shot groups as small as 2.5" at 50 yards with different specimens from a bench rest (not a machine rest). Not too shabby for $1,195.