Ok just my opinion but i know the padi machine will weigh in here but wtf.
Nah, it's about the PADI machine. There's huge morons in both agencies, and no, TDI is nothing "more onerous on the qualifying criteria". Their programme is nowhere near "rigorous training" or whatsoever.
About "get a TDI or IANTD instructor and you will probably get someone dedicated to teaching technical diving", well, my OW instructor was a RB diver, he also was a TDI instructor up to at least ANDP, he's considered a good instructor in the area, and he didn't know how to calibrate his RB. Scary huh? Oh, his RB cert was also from TDI.
IANTD... maybe, but they're a step above TDI in the difficulty of becoming an instructor from what I understood, hence you're less likely to find a crappy instructor there. I said less likely, not impossible. Even GUE could **** up.
Long story short, look up who your instructor would be, does he master the skills he's supposed to teach, and does he teach them well? The agency doesn't matter that much imo.
I also honestly won't care about the "find an instructor that does only technical diving way beyond the level he teaches". Many deep divers look like some sort of seahorse-octopus and are considered to be very good, I know that I won't train with them as their view on diving doesn't align with mine...