Vogel's are the big name custom boots in the Hunter and Jumper world. (George Morris endorses them.) They are roughly equivelent to the Dehner's. I've owned both custom made Vogel's and Dehner's and had terrific experiences with both.
I did also have a pair of DerDau's made, about 25 years ago. At that time, they were considered a slight cheaper option for custom boots with less wait time than either the Vogel's or Dehner's. I still have them; I have elastic gussets put in them a few years back as I had them made when I was thin and fit. The story I vaguely remember is that the DerDau guy was an apprentice at Dehner and then went out on his own? I was perfectly happy with them but obviously customer's more recent experience in more relevant.
Journeymen in Middleburg used to make custom books, but I don't know if they still do.