I assessed Wycombe Air Centre for a cadet scheme for a former employer - I was very impressed with the organisation, prices, quality of the aeroplanes, and quality and attitude of the instructors.
I did a less thorough assessment of Airways Aero Association - a little more expensive, and a little less well organised - but still basically very good, and very well spoken of. Certainly a better choice of aeroplanes.
Basically, you're unlikely to regret either - so visit them, get a trial lesson with each, pick a simple inexpensive aeroplane to learn on - and decide which one you prefer. It's a choice of good or good.
G