Widescreen, of course. To get a film into a 4:3 area -- usually even a 16:9 area -- there has to be one of a few compromises made. The most obvious one, and the one that does nothing to alter the image, is to letter box it. This allows the entire image as seen in theaters to make it to home TV sets. Full screen movies do one of two things instead; they either crop it down, cutting off about half of the image, or open up the matte, adding things we were never supposed to see -- such as boom mikes. There's also the option of anamorphically squeezing it, but that looks so terrible that it hasn't been used since the very early days of VHS.
There's some good example images of what I'm talking about at This page [http://www.widescreen.org/examples.shtml], along with further discussion of the issue starting here [http://www.widescreen.org/widescreen.shtml]. Pay special attention to the pictures from Labyrinth -- at least two of the cropped images have scene critical characters cropped right out.