In reply to ripper:
There isnt a simple answer.
yoga in particular has so many different variations that give very different results. Bit like going "climbing" and having a choice of going up everest or doing autobelay session.
Pilates, as I understand it, is in theory more structured but in practice instructors vary massively as well.
Personally I have ended up with yoga mostly due to a couple of really good instructors but if I moved elsewhere might well end up doing pilates instead.
Best to go along and try a few to find a type which suits you.