I have a question and a follow-up question. I love my instructor and believe she is doing a great job. I have learned a lot. I have also read a number of posts here where the response starts with "If you had a better instructor..." As a newbie, how am I to know for sure that my instructor is great or the best one to teach me? How would I know the difference if I have no comparison other than the internet? I can find multiple opinions on almost any topic on the internet.
If you've learned a lot, I would agree with you. The role of the instructor is to teach you all the required skills to a reasonable comfort level. If you feel you are comfortable with all the skills, then I'd say your instructor is at least doing a good job.
I'm also of the opinion that different students require different competencies in their instructors. There are some students who take to the skills quickly without much need for correction, instruction, and repetition. These students can easily get by with a lesser instructor than a student that really struggles with some of the skills.
I'm not an instructor. I feel I would make a terrible instructor, but maybe not. I was one of those who did not have any trouble with any of the skills in OW, or really any of the other courses I've taken since. My daughters were the same way. Knowing I'd probably make a terrible instructor, I did not even let them breathe off a regulator in our pool until they were done with their OW certs.
How do I know that I am getting the best instruction available?
Are there compelling reasons to use different dive shops and instructors if I am happy with the one I am currently working with?
I don't know of anyway you would know that you are getting the best instruction available. It should, however, be quite obvious when you aren't getting adequate instruction. This is when a change is needed. If you are happy with your current instructor, I really see no reason to change. If you are struggling with certain aspects, then a different instructor may be able to approach it differently, and that might be what it takes to make it click.
My original OW instructor was less than adequate. I still managed to do the skills quite easily. A lot of it came from being very comfortable in the water. The only checkout dives I did in that first course was over one day (maybe two dives) in a max of 8-10'. I had a scheduling conflict, and couldn't do the river dive (again, shallow), so did not get any actual swimming time with the gear. I left that course with an OW cert, but I didn't really feel comfortable.
So, now I have two OW certs. My other OW course was a complete 180. Lots of pool time. Course was over 6 weeks, and we were in the pool at least 4 hours each week. 5 checkout dives in the Keys. Much better, and I left that course a lot more comfortable with diving.