I'm studying at Prestwick Flight Centre and for the most part it's good - good instructors, the aircraft seem looked after, good R/T experience and experience working out of a 'proper' commercial airport and all that entails (controlled airspace, larger aircraft, helicopters etc) and it's not badly located for me (25 mins or so from home to the airfield)
On the negatives, it's expensive (but so is everywhere in Scotland compared to many schools / clubs down south for some odd reason) - this is alleviated slightly by block booking (usual caveat applies - use a credit card) - you'll also need to pay membership, landing fees (which are higher than at smaller airfields but surprisingly less than Cumbernauld), and the airport themselves for security check and an airside pass.
Finally, and somewhat frustratingly, they're now down to two aircraft that can be used for training - meaning availability of the planes isn't ideal - this is the biggest concern I have at the moment.
PM me if you want to chat further, I was in the same boat as you a few months ago and went through the same choices. If you don't care about the possibility of doing Night Ratings/IMC etc and are just looking for flying in daylight VFR - go to Strathaven and try their C42 - it's a lovely aircraft to train in and they're without a doubt the nicest / friendliest airfield I visited when looking into this at the start - I still keep contemplating seeing if they'd let me base a small C152 or C172 there in the future
Hope this helps a little