I know I'm late to this party but the film was actually filmed in widescreen but Kubrick mandated it be shown on home video/laser disc/dvd in full screen. The box set that was released 10/23/07 is the first time a home viewer can see it in the original wide-screen format. Do your research.
No, the film was filmed in "open-matte" format, and Kubrick prefers the 4:3 format. But he's dead now, and WB has saw fit to release the film in 16:9 format on HD discs separately and on standard DVD within the Kubrick Collection.
Apparently when Kubrick viewed films on a standard 4:3 TV, he disliked the fact that "black bars" were visible and mandated that home video releases of his movies be released in the 4:3 Academy standard to eliminate them. This was before 16x9 TVs existed, and as such the new DVDs have been reformatted to the original theatrical ratios to better suit more modern display equipment. It seems that Kubrick preferred height to width, but if he were still alive today I don't feel he would object to the 16x9 framing, as it was the way the films were seen theatrically. If you consider that, one could argue that either option is more "correct". I would say just purchase whichever version fits your display and be happy with it.