The "best" in my opinion for just a sole reference source is the Ford factory manuals. But keep in mind that's several different manuals- the shop manual for the general overall vehicle; the Emissions book for how everything works, and the EVTM and big wiring diagram for things electrical. And there's also the training manuals for the new things as they appeared, which are really cool.
Aftermarket sources, such as Chiltons and Haynes, have value in that their material is presented for the "casual" mechanic, the "do it yourselfer", versus the professional perspective of the factory materials. One value of the aftermarket resources is their describing procedures with generic special tools, versus the Ford books refering to "Rotunda tool number xxxx". But, the bad is that they just skim each subject, and are very vague in many places.
For what it's worth, before I dive into something new on my trucks, in order, I a) search the (old & real) TRS.com forums, b) read the Ford material I have, and c) read my Chiltons and Haynes.
Searching the TRS forums was actually the most valuable resource for me personally.
Just my humble opinion . . .
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