mac,
1. The instructor determines the quality and integrity of the material presented during your course. Therefore, regardless of which agency the instructor represents, they are the single most important thing you must seek out. Truly good ones who are compatible with YOUR personal needs often take some finding. That's why people say what they say.
2. There are only something like 32 GUE instructors on the planet. Their quality control is thus a tad easier than some larger agencies. Additionally, there are a few other things that factor into GUE instructor selection.
3. The GUE DIR-F is not a technical course. It is a course about fundamentals of diving. The fundamentals apply to all diving, both recreational and technical. It has been stated more than once that most of what is taught in the DIR-F appears within the first two chapters of the PADI manual. The goal, however, is to learn to perform fundamental abilities with precision. Any diver interested in being a better diver could learn something from spending a weekend focusing on fundamentals this way.
4. Perfectly good technical course curriculums are offered by IANTD, TDI, NACD, and several other agencies. GUE also has excellent curriculums. People learn things differently. This is why how the material is presented and by whom impacts on how much students take away from their training. You won't be ill-served by a course offered by any of the above agencies. Exactly how much you get out of the course, however, will depend less on the curriculum or agency, and far more on HOW the instructor presents the material to you in a way that makes most sense to you. Some of it is intuitive, but some isn't - and having an instructor who can effectively communicate abstract concepts so that you grasp them can make all the difference in the world with respect to what you take away from your training.
If I were you, I'd start by going to websites (IANTD, TDI, GUE, etc.) and spending time reviewing the course standards and criteria (published on all websites) for their technical training. This will tell you much about the curriculum, equipment requirements, prerequisites (iow, order of courses required) etc.
Finding a compatible instructor, which is the more important part, takes a bit more effort. Places such as this one are a good place to start.
Best of luck,
Doc