If I were doing it over again, I'd want a school where I could sit down with an instructor at the outset and work out a realistic target number of hours in which to complete the PPL. I realise there are many variables involved, but there were a lot of expensive wasted hours in my training.
Proper briefing/de-briefing, not just a few hurried scribbles on the whiteboard or - worse - none at all and an instructor who's out the door for lunch quicker than you can drop a dish of hot lasagna.
I'd also want an instructor with the foresight and manners to call me when lessons are cancelled
Any school willing to teach me how best to use a GPS and modern navigation planning tools (even if only at the most general, introductory level) would also get my vote
Yep, mentoring. Post-PPL you can easily fall into a black hole.