Both are good, however Dave's is half the price, and a lot more thorough.
Caleb's is by no means bad, but he only really runs through settings and functions he uses, whilst Dave goes through every function on the menu's. Even if it's a a photography-only setting, he'll still mention it, and also talk about it if it relates to a video function, or a setting that might effect your video footage in some way.
Caleb's is more for people who are already familiar with DSLR functions, filming, and terminology, whereas Dave's is more a true beginner's guide. He'll run you through exposure's etc, but also show you how to do it multiple ways, specific with the GH4, and also how each method compares to each other and their results.
Caleb's also wastes a chapter on accessories (tripods, monopods, etc). Whilst not a bad thing, it's not GH4 specific. They're general DSLR accessories that Caleb himself has posted plenty of reviews on that can be viewed, for free, on his website.
Caleb does talk about a few things that Dave doesn't, like: Using adapters on non-panasonic lenses; importing and basic editing on both FCPX and Premiere; and also some small editing tips on how much better 4K is to work with than 1080p, if you have slightly overexposed or incorrectly white balanced footage, which I found hugely helpful.