The first two lenses are MILES away from that third one. It's like comparing a pair of vipers to a civic
The af-s 18-200 vr is the ultimate walkaround lens from nikon. The first one is a good walkaround from nikon. If you're getting the 18-200, save your money and skip the 18-70.
AF-S: auto-focus silent, it's the silent wave motor that zips the lens in to focus damn near instantly. Major major asset. I'd weep with joy if I could get it for my 50mm f1.8
IF - internal focus, means nothing outside the lens moves when focusing. Another asset.
ED: ultra-low dispersion glass. It's way good ****, better clarity and contrast.
DX: won't work on film.
VR: vibration reduction, lets you shoot sharper handheld (sans tripod).
The third one is cheapest because it's made out of crappy glass, has no AF-s or ED glass, or VR.
best lens is number 2. Period, don't let anyone bull**** you