I very much agree with the comments made by titch. I wouldn't suggest taking several trial lessons, but I would strongly recommend visiting as many airfields as possible. You might be surprised (I know that I was) at how shambolic many GA organisations appear to be. As an aspirant PPL, you are effectively walking in to a business clutching a bag containing several thousand pounds which you plan to give to that business. It's surprising how many of them greet you with a "yeah, whatever" attitude.. .. .I am not suggesting that smooth and smarmy customer service is a necessary indicator of quality or the thing to go for. It's really a question of how enthusiastic, how passionate even, the training organisation appears to be to an enquiring outsider.. .. .It is difficult on a short visit to judge the quality of the instruction, or the maintenance standards of the aircraft, but a little time spent hanging around the school may give some clues as to both. In terms of organisation, are the lesson slots too short and too numerous, so that lessons overrun and instructors have no time for proper briefings and (importantly) debriefings? Does the school seem more interested in the low-effort business of trial lessons/disguised joy rides than in its committed students? Look around the club house: do you see instructors chatting about flying with their students, or are they rushing to the next lesson, or sitting together telling disparaging tales about student X or student Y? Are there quiet corners or rooms for briefing, study and planning?. .. .As for large/small airfields, the larger ones give you experience of full ATC operations and allow rapid development of R/T skills, but you spend more time taxiing and holding, and, at the early stages, have the additional pressures of fitting in with traffic and controller requirements whilst struggling to manage the aircraft. Elstree, by the way, is physically tiny, but is busy and crowded.. .. .Enjoy your course, wherever you do it.