It’s an often heard question and a debate that seems to have no end.
I was asked to write an article about my take on it for my favorite onLine diving magazine: X-Ray. And rather than reproduce it here, opted instead to have you link to the article itself since — just like always — they did a great job of making it look good. Enjoy
Doppler's Tech Diving Blog 
Instructor is important in diving rather than agency because without instructor there will be no agency at all. But it is also important that a dive instructor should also be registered and certified for us also to ensure our safety.
Instructor, all the way, especially when you go the tech route. I researched each of mine in-depth and never chose a single one based upon agency or even nationality.