I've been looking at several flying schools recently incuding British Airways Flying Club who i have heard have been recently bought out by another company (although i'm hoping someone else can confirm or deny this) and Cabair who i understand are a much larger and corporate organisation.
I'm based at Wycombe Air Center (opposite BA), I cannot tell you what they are like in BA but one thing i do know is that their rates are considerably higher than those at WAC & you very rarely see their instructors flying.
Cabair is a large organisation but if u choose the right school you get a very good service with the feeling of a much smaller friendly atmosphere. in my opinion Wycombe & Denham (I have studied at both) fall perfectly into this catagory. You get the assurance of a large organisation with regards maintenance & service but also the friendly nature of the small school!!
My choice would be Wycombe OR Denham every time!!