GUE is for people who think the system is appealing; UTD is for people who think THAT system is appealing. For either agency, progressing through THEIR classes makes the experience easier.
I would say that is with any agency. Each one seems to have a different emphasis or style or what-have-you and each diver, I think, needs to find the "agency path" or "agency mindset" that suits their personal diving goals and mindset. And within that framework, find an instructor who meshes with their personal diving and learning style the best.
Found this old interview with Bob Sherwood where he compares it to choosing a path with Martial Arts. (The audio should drop right at the spot, if not, it starts about 10:53 and runs for about one minute, before the website plugs start.) I think the comparison is accurate.
PD17: GUE Fundementals Class with Bob Sherwood (audio interview for Pod Diver Radio) - YouTube