r/Glasgow Tools

I did a PPL at Cumbernauld, although the school went bust several years ago (fortunately after I qualified). I think there are two fixed wing training organisations based there at the moment, but they do tend to change every so often.
My comparison of the different locations:
Glasgow - too busy
Prestwick - less busy, but you'll still have to deal with big airport stuff (taxi clearances, waiting for wake turbulence, etc.), better weather than the others (usually) so you probably won't spend as much time sitting around waiting for clearer skies
Cumbernauld - OK, it's a little higher up though, so sometimes the cloud is too low for even doing circuits, it's very rare to be delayed by other traffic
As for choosing a school/club, try a few hours with each, and go with whichever one is best for you.
Finally, **DO NOT, UNDER ANY CIRCUMSTANCES, PAY FOR FLYING TRAINING MORE THAN A DAY IN ADVANCE**. Many flying schools try to improve their cash flow by offering discounts if you buy blocks of training hours, rather than just giving you a bill after landing. If they go bust after you pay, but before you fly, you will likely never see the money again. The only time I'd recommend you take an offer like this, is if you turn up first thing in the morning wanting to get several hours in, the weather forecast is excellent, and there's an instructor and aircraft free all day, and you only pay for that day's flying on that day.