cjm's question is a good one - I found my flight sim really useful in making progress, particularly with circuits, PFL and the like. You can use FlightGear for free, or pay a little for something else that has nice stuff like real terrain pictures. Get yourself a proper yoke and pedals, though - eBay occasionally has some. A joystick is a bit of a waste of time.
During my power training I stuck to the same instructor for almost all of it. On the occasions when I took somebody else (when my usual guy wasn't there) there was definitely a long-term benefit - emphasis on different aspects of some things - but I was also aware that I didn't make anywhere near as much progress.
Have you had 3 instructors because you're not available, or because they're not available? Might be worth talking to one of them and trying to synchronize a bit.
Edit: And don't be afraid to be picky - you are, after all, paying quite considerably (or somebody else very generous is)!