I started the trail with two - TWO - trail guides ! Craziness. But I was unsure as to which would benefit more. I can assure you , it did not benefited to carry two.
WORTH THE WEIGHT:
The Thru-hiker's Guidebook by "AWOL" Miller. The elevation maps and shelter mileage are great.
The Thru-Hiker's Companion --AMC
I had planned on mailing this back to my dad so he could follow along, but I met some people who were hiking with nothing at all and had no idea how far the next shelter or town was at any time. So I just gave it to them. Less weight for me, more info for them.