I'm a student at AeroMadrid and I have to say I haven't heard of any problems concerning delays with flight training.
As for comparing schools... everyone should come to Cuatro Vientos and check all the schools. As far as I'm concerned, there are only two "real" schools here. AeroMadrid and American Flyers. That's all I can say.
ATC is in spanish but they will always reply in english if contacted in english on the first transmission.