Just chipping in.
I did my instructors course at Denham, and do my hobby flying at White Waltham. Both are well run, have good condition aeroplanes - the social side is better at White Waltham. In that vicinity is also Wycombe Air Park (which I used to have an aircraft share at), similarly good for training and possibly the best of all of them for airport facilities, but fairly non-existent for the social side.
You haven't really got a bad choice there, go do a trial lesson at each, and decide which feels best.
G