I did an Aerobatics course at Leicester on the C152. That sounds like a rubbish aeroplane to use, and it is. But it also teaches you to really fly the aeroplane rather than relying on power to fix things. It makes aeros in anything more aerobatic much easier. It has certainly served me well.
Dave Biddles is an excellent aeros instructor in any aeroplane (C152, Slingsby or anything else you send his way). He really does know how to coax the best out of n aeroplane and pilot, plus he's bloody good fun to fly with.