Which Ruger .45 are you looking for? the P89 series (my brother has one, very nice fit/ feel, and shooting) are good reliable pistols as long as you maintain them properly, like any other firearm. Accessories are kind of short when it comes to most of the Ruger Auto's, when compaired to either Glock's, 1911's, or some of the other police/ military issue side arms.
My personal taste for .45's runs in the 1911 family, and there are just TOO many good choices there. But the best thing about the 1911 series parts are fairly interchangable, and a so-so pistol can always be customized into a tack drivin beast.
As for AR's, I have a bushmaster XM15 16" barrel, I know it is good out past 600m for accuracy (further than I can accurattly shoot open sight at least....) As for reliablity I've shot hundreds of rounds thru it and had no problems I could blame on the rifle, Magazines are the common failure point of most AR's. An other problem is short barrel versions haveing short gas tubes, which can cause cyclic problems. Although I have heard that the piston conversion models don't experiance this problem, I haven't played with one yet..
With the AR series of rifles you can find just about anything you could want to hang on it, and once you have a lower reciever you can swap uppers out for different barrel lenghts or calibers with very little problems.