Stapleford...............good reputation
Denham pilot centre.................. I have had no dealings with but they have not attracted any adverse comment in this forum.
Firecrest......... nice people at an airfield with a circuit that covers most of Herts.
Airways flying club at Booker............... the "all in" pricing structure at first look covers up the very good value for money that they offer.
North London Flying School @ Panshanger.......... the Pprune search engine is your friend !