Impossible to answer!
For decades it was the Nobler. Mainly because almost every plane to win any major contest was either a Nobler or a Modified Nobler. Many, many guys built Noblers with different shapes and named them Olympic, Gypsy, Venus, Sabre, and such. One great pilot down in the Lone Star state drew around a Nobler rib, changed the tips and all a touch and won the WC with it and his pipe (which wasn't the CF tuned variety).
I doubt that any single design will ever be able to overcome that record, but a "Nobler" is not competitive today at the top levels of stunt.
So far the very best flying (all around) stunt plane I have flown was my USA-1. Billy Werwage did close to 30 years of damage with his and his derivatives of it (Junar, Geo XL).
Bill <><