Not used one for a long time, but ESF generally run the French ski school cartel, and are like a factory churning out skiiers. My experience for myself was impatience and rudeness from the instructor. That was as an adult though. I got a far better experience in Austria.
Outside of ESF, there are the independents and “foreigners”, i.e. Brits. Have no recommendations though.
I’ve used independents for a few years now as I got fed up with how poor ESF could be. However it is very dependant on the individual instructor but I had more luck staying away from ESF for my daughter. Can’t recommend a particular school though, sorry