I have no official figures for you but my estimate for Eurocontrol would be around the 60% mark, quite similar to NATS.
However, any controller will tell you that the actual figures vary wildly from course to course. It then becomes difficult to come up with an average because you need a larger sample to make the figure accurate. This can never happen because training courses are reviewed, adapted and changed on a regular basis.
It all comes down to the selection pool you were taken from and a little bit of luck.
Whichever you choose it'll be a great life and there's always the possibility of moving around the world to find somewhere you like!