SimFlyer,
I think you will have realised by now that there is no magic answer to your question!
A school can look great but provide poor service and instruction. A poor looking school, however, might have some great instructors to offset poor administration or minimal facilities. Of course, the only way to find out for sure is to try one out for a while because even the trial lesson might not give you a full picture.
This is another VERY good reason for not concentrating too much on cost and for NOT paying up front for seemingly attractive package deals. Paying as you go gives you maximum personal control and flexibility.
Unfortunately, travel distance is a very limiting factor in terms of choice and airfields closing is as big an issue, if not bigger, than flight schools closing!
Travelling back and forth over an excessive distance could quickly dampen your enthusiasm, not to mention eating into your budget! So, you need to balance a number of factors.
My opinion, for what it's worth, is that the quality of instruction is the number one factor. I have flown with a number of instructors over the years and all have been good to excellent. Most enjoy teaching and want you succeed whether "hour builders" en route to the airlines or full timers (or old full or part timers!). So, whilst having the one good instructor throughout might be ideal, I would not get too hung up on that issue either because the syllabus is set down and you will have your logbook to record your progress irrespective of the records that the school and/or instructor might keep.
I do totally agree that a good lesson should consist of pre-flight brief and de-brief so it is probably a good question to ask in order to inform your decision making. A one hour lesson, therefore, should probably amount to two hours. Anything less might raise questions about instructor pay and employment arrangements! So, expect to pay a minimum of £160 per hour for lessons in a Cessna 152 (e.g. £100 for the one hour use of the aircraft plus £60 for the two hours instruction). This may, or may not, include a landing fee, so it would be worth asking about that. Also whilst most organisations use a "Hobbs meter" (essentially engine start/stop time) for invoicing, I have come across other methods, so check that out, too. With "Hobbs", long taxying times or other delays can seriously eat into your "air" time for a given "hourly" rate so flying at busy commercial airfields can work out quite expensive in the long term.
Finally, margins are very narrow in the aviation business and there's an old saying that the "old hands" on here will know well and it goes; "If you want to make a small fortune in the aviation business, start with a large one!".