Two of the most difficult artists the Orchestra I'm in worked with are:
2. Judy Collins (She wears the diva- b*itch label proudly)
1. Kathleen Battle. Ms Battle is on a whole other level of difficult.
Interestingly enough, the best quest artist, in my Orchestra career, by far, was Beverly Sills. A lovely, gracious woman that was a joy to work with and could flat out sing.
HsvHeelFan