First one, just looks abused to me. Poster can't even pump up the rear tire for the picture? No mention of size so why bother with a bike if you are not sure if it fits?
Second one mentions size and looks nice, well maintained. Not to mention the threadless stem means it's more than likely a new model than the third one. Also has v brakes whereas the third bike has cantilever, old style mid 90's mtb brakes.
If for some reason you have to change the stem on the third bike, good luck finding a quill style stem that fits.