I have both and I use both. You are also getting stuck with my recollection: I have spent the year draping mostly and the only flat pattern work that was not modified from existing patterns has been from Muller und Sohn's books (in German no less), Moda Aloi - Il Taglio del sarto moderno (the book in Men of the Cloth and in Italian) of which both of these are men's tailoring and ethnic Indian clothing. I have not touched these books in over a year because of what I have been doing, so take it for what it is worth.
Crawford's is a good stand alone, Furrer's works perfectly with her Craftsy classes and is a little more technical. Both are by far more superior to the college textbook they push from Armstrong.
Both cover about the same amount of patterns. Both are excellent teachers. Furrer uses her own ruler instead of several, which while not necessary for her system is a good tool, and can be used with any other system. I've used it with what I have worked with, so it has a use outside of Furrer's teachings.
It is also easier to learn just one system before trying to add to it...so I would suggest you pick one. Thing is, if you're going to do Furrer's Craftsy classes, then I'd go with her. And they are wonderful classes. If you are not a Craftsy person, or use University of Fashion, then go with Crawford.