Answer by Andy Bradford:
I spent about 18 months getting my PPL and had about 7 different instructors over the time and still did it in just 3 hours over the minimum 40 hrs at the time. I found the variety of instructors a help rather than a hindrance as you don't get stuck with 1 instructing mind set. Don't forget, most instructors are low hour pilots just trying to hour build before going on to an airline job. They aren't necessarily good teachers. So if you take your time to learn (you get to experience flying in much more weather that way) you are likely to go through instructors at quite a rate anyway.I did however learn on only one type of aircraft and my training was based on one airfield (other than required land aways and cross country). While I'm sure that learning from different airfields would be a big bonus (variety of experience is always good), I can't say what effect learning in multiple types might have. I can see advantages in sticking to one type.