I think Snap-On's program is called Mitchell on Demand. AllData was created by Motor. I never cared for Motor manuals and hated it when they took over Chilton and ruined their shop manuals. But, AllData has got progressively better through the years and seems to be the standard for independent shops now. I can't speak for the personal version (where you buy a subscription to your car only), but the shop version has pretty decent info on 82 and up Mercedes. Not as good as factory Mercedes manuals, but better than a lot of the other offerings. You can view a demo of ALLData at
http://www.alldatapro.com/includes/main.jsp. It has everything that the shop version has, but only for a 93 Ford Ranger 4.0L. As for the Haynes, it leaves a lot to be desired, but the schematics are worth the price of the manual.