I have purchased several TankCraft books which are nice but not great as far as building and details.
Jentz & Doyle’s Panzer Tracks series proves outstanding. Museums are known to use PT as reference to get details accurate or craft replacement parts. Their other books are outstanding as well.
Achtung Panzer #4 is my favorite Panther reference for building. It’s out of print and sometimes hard to find. Basically all major all Panther models are well covered. If I could only have one reference to build with it would be this one as it covers Panther D, A, G, F, II, JagdPanther & BergePanther in excellent detail. It isn’t perfect on some hair splitting details but it’s good enough for ~99% of what I need. For accuracy I’d differ to Jentz if there’sa question. For overall usefulness modeling I prefer Achtung Panzer.
Panzers in Samur while pictures of museum vehicles is also very useful for model building. It isn’t quite as good on hair splitting details but when working on a Panther or King Tiger proves useful.
The issue is really finding the best references on the prototype subjects and then being able to translate the prototype information to your model project.
Subject modeling references, of necessity, must focus on building this or that specific KIT which may or may not be the most accurate starting point. These sorts of references also become dated very quickly as the inevitable better, more accurate kits of the same subject are released later.
So, I submit that the question you really should ask is, “What are the best references for the King Tiger and Panther tanks?” My answer to that would be any of the Jentz and Doyle books on either of those AFVs.
For the Panther G, I’d submit that you want a copy of “Panzer Tracts 5-3.” This will be hard to find new, but you can get it used.
As an alternative, I would suggest the Kagero books, 7043 or No. 11 (out of print).
For the Tiger, you should look for a copy of “Tiger: VK45-02 to Tiger II.”
I’m sure that many others will chime in with their recommendations, but in general, I suggest that you look for the newest published dates. There are many older references that are still pretty good, but the state of knowledge constantly advances.
The best modeling books are the ones that focus on techniques, methods and skills which never really go out of date. The Osprey modelling series of books are all generally quite good and the techniques in most of them can be used across many different subjects, so their books, say, on German or US armor are equally good no matter what you’re building.
The Panzer Tracts website shows 5-3 as, “Coming Soon”.