GUE is the only agency that has what seems to you like a "doctrine"? Okay, sounds like you have made up your mind in this regard.Just being honest here.
An instructor affiliated with any of the major tech training agencies will get you where you want to go. The differences really do come down to the quality of the instructor, not what agency is listed on the card. You have probably seen the maxim in other threads: "It's the instructor, not the agency." There are even instructors who teach for more than one of the major agencies (and I would include RAID and GUE in that group, though they are smaller than, say, TDI), and you get the same quality instruction from such an instructor regardless of which agency's name ends up on your card.