What is the best paradox you have ever heard about?

Russell's Paradox because it is legitimate. Mathematicians have thought that every paradox was a fallacy they have moved to Axiomatic Set Theory even though it has problems. But it is incorrect to to think that every paradox is a fallacy and The Russell Paradox proves it. I worked on The Russell Paradox hoping to get some insight why it was paradoxical. I broke it in to two opposite sets with respect to the paradox. What I found instead was that each those sets was infinitely nested, meaning that the only way The Russell Set could have proper "Closure" (math term) was to seal itself with a paradox. This was the first non-fallacious yet a genuine paradox I've ever seen; it gave me a very deep respect for Cantorial Set Theory.