Best flying is at Perth - no doubt. However, from Glasgow I would seriously think about travel time and availability of aircraft. Strong advice would be to look at PIK. Nice bunch, always available and easy to get to. My personal experience of Cumbernauld is not great but you should go and look - its a bit, agricultural?
Leading Edge also operate at Perth but I've heard all sorts of gossip so check that out too. Tayside used to be very good but Dundee isn't easy to get to and Fife worse. Instructors are sometimes a bit arrogant - for no good reason. If they still do the RAF flying scholarship - get used to waiting!