Heres my 2 cents, and take it for what it's worth.
Though I will agree for the most part with what everyone has said, I will disagree to some extent.
One being, that there are so many factors to what is considered a "good" instructor.
For example my OW,AOW, and Rescue instructor. For OW class took much more time than that of classes I've sat through recently as a DM candidate... However, I see the students going through the shorter classes retaining more knowledge, and scoring higher on quizes and tests. I would also consider my OW instructor a better instructor, for actually going over ALL the material at least 2-3 times and in more depth. Of course it's hard with an OW class anyways, so much to retain and the classes are so short to meet what students want, inexpensive, and short.
Now, as "good" as my OW instructor was, when it came to moving into "tech" type stuff, I could tell IF he could teach it, he wouldn't be suited to teaching it.
He in my opinion was too close minded about how one dives.
Also, PADI for instance seems to have a not so good name in the tech classes, I'm not sure exactly why, other than from my understanding that PADI has only recently become involved in the "tech" classes, just recently finnaly adding a Tri-Mix class, which I have yet to hear of an instructor/student for it.
Also, from my understanding, here in Oregon, and possibly Washington, there are ZERO PADI TecRec Instructors, there must be some sort of reason?
Almost EVERY PADI shop here advertises the TecRec Classes but there is no instructor in the state from what my MSDT Friend tells me. There is however several TDI/IANTD instructors, many of which I hear are VERY good.
Also, keep in mind for an instructor to be good, they must actually be doing dives in which they teach, in a non teaching environment... many PADI instructors hardly dive outside of teaching period, let alone do tech dives (just the nature of things). Something else to consider is that to become a DM in IANTD one must have been through more "tech" like classes than PADI, and my MSDT friend who recently completed IANTD Deep/Adv Nitrox and is starting TriMix said he learned more in his Deep/Adv Nitrox than in his DM class through PADI.
As far as experience, I don't fully agree with the "100" dives, I think 50 is an ok number, but then again, I think it's more how you are in the water, skill wise, comfort wise, etc.
Considerations are, how comfortable you are now, how is your air consumption rate in comparisson to when you started, how deep of dives have you averaged, if you've only done 20 dives in 30' I would say, you need some more expereince a bit deeper... That said, I think for MOST divers 100 dives is an adequate # to get the appropriate experience, and is a good number, however I've seen divers with 20 dives who are far superior divers to those of more than 100 dives.
Absolutely nothing wrong with Nitrox at any level IMO, it is a simple tool, and easy gas to use, even after use of active use, it is still sold as a semi-dangerous gas, but in reality is very safe gas, and in my personal opinion, other than cost leaves little reason for diving 21% air.
In the end I would say instructor deffinately does a lot more for the class than agency, PADI has some of the best materials around, however many of the must take a class from "tech" instructors are TDI/IANTD and it sounds like PADI is laking in the "tech" classes.
Just my 2 cents, and views reflected from opinions I've gathered from others on and off this board.
Enjoy your diving, and welcome to this grand sport (20 dives ago that is)
