Why Is It?

I've got a couple of 4" thick OLD Motors Manuals that were my dad's. Some priceless Info in those.

Yep, Motor's for the win.

I had a friend in HS that had Chilton's.
I bought a Motor's at a yard sale after using them in auto shop class and we were blown away by how much better and more specific the Motor's was.
Plus there's the cool "identify the car and sub-model by the grill" section headers.

Chilton is a good second choice, though.