Thank You for Your input!
Yes, I already did a trial lesson and talked to people at A and C. Visited B and plan to do a trial lesson there soon.
A and B are non-profit flying clubs, that means the instructors do it in their spare time or at the weekends. You have to join the club and do a certain amount of work-hours for the club during the year. But its much cheaper than joining a commercial flying school like C.
What do You think about the Diamond Katana as training aircraft for basic training? Most schools still seem to use the C150/152 or C172...