"Favorite" is a funny choice of words when it comes to describing one's mistakes. Because believe me, I've made a lot in only twenty years of living.
I now use the word 'favorite' very cynically in stating my favorite mistake to be when choices I made resulted in losing the person I would deem to have been my soulmate. Why? Because it's the only mistake that, when I'm old and senile, I'll still go to my deathbed wondering about the what if's.