If you're in Ayrshire, really Prestwick is the place to go, it's not particularly cheap flying but by the time you finish the course you'll have a lot less trips to Glasgow/Cumbernauld and that really does add up.
I only know instructors at the Club and I have only good things to say about what I've seen. It's all very informal which may or may not be a bit frustrating but the instruction will be from really very experienced guys doing it for fun, you'll learn a lot more
. That said I'd doubt you'd have a bad time at any of the schools within a sensible distance from you
.
As for CPL. I'd keep my mind off that for now, there's a long way between PPL and CPL in terms of flying (and exams!).
There's also a 3-Axis microlight school at Strathaven if I'm not mistaken, something worth considering as well
.