Although I have a familiarity with some of the mentioned organisations and did my initial training with RAC/RNAC, it was all a long time ago so I don't think that I carry any baggage .. and, of course, the organisations and their staffs will have altered in the intervening period.
The priorities listed in the previous posts are all relevant but consider some other thoughts which I suggest are of fundamental importance -
(a) is the student advised to establish his/her bank balance so that the initial training can proceed at a sensible pace ? If you do an hour a day, then you progress much faster (in terms of flight hours to achieve a given standard) than if financial constraints make it an hour a fortnight. Likewise, are you encouraged (pushed ?) to get your theory exams done ahead of time so that the absence of necessary bits of paper doesn't delay your flying progress ?
(b) is there a comparatively high ratio of high time experienced instructors to junior instructors ? This has a bearing on mentoring, standards, and product quality control generally. The ratio of total instructors to students is, I suggest, of little relevance affecting only the workload that the school reasonably is able to undertake. If there are insufficient greybeards, though, then the supervision and mentoring of the junior instructors has to slide.
(c) are in-flight instruction hours matched by detailed preflight briefing and postflight debriefing sessions ? If you want good value here, expect to pay for it separately or be prepared to accept a higher instructor cost component in the dual flight rate. Certainly, if you get a hold of some good instructors, the learning value in the briefing sessions costs far less than slower progress in the air.
(d) for ab initio training, is a country airfield preferable due to lesser traffic density, airspace considerations, transit time to the training area, etc. ? Contrary-wise, is the city airport preferable in the later stages of training for just those reasons ?
(e) does the organisation's instructor staff pander to the student ? ie is the operation principally driven by the almighty dollar ? .. or is a bottom line attitude, flight standard, and sensible rate of progress emphasised ? What is the average time to solo and licence (considering frequency of flying) ? If the average student takes forever to solo, then something is not right.
(f) is the student able to complete a significant proportion of his/her training with only one or two instructors to minimise unproductive time spent by the next instructor in coming up to speed with the particular student's problems ? Does the school emphasise the use of extensive and constructive student progress records ?
(g) is the unserviceability record for the school's fleet acceptable. Does the school's system approach defect reporting and rectification sensibly and in accordance with the regulatory requirements ? .. or do you regularly find that the aircraft departs with a bunch of unknown, carried forward snags ? I wouldn't worry too much about fancy gadgets in the early stages, but this becomes important for later training.