I'm surprised about is that no one has mentioned that different types of instructor suit different people.
Personally I'd much rather have the quiet instructor who only prompts me when I haven't worked out my own mistake rather than the more military style of pointing out exactly what I've done wrong the second I've done it. I'm certain there are plenty of people of the opposite persuasion...
As it happens, when I did my PPL the instructor I had was absolutely brilliant for me and always gave me a chance to identify my own errors before he pointed them out. He was a "grey hair" and had a great deal of experience and I think this had a lot to do with his outlook.