This basically sums it up. I can only go by recent performances and recently these three have been slaying. Babs killed "the way we were" on Oprah last month. Tina sounds good as well, but if you youtube Gladys, Babs or Donna you will see they still sound damn near the same.
Chaka's recent performances have not been good. Neither have Miss Ross's. And she's actually my fave on that list. Aretha sounded good when she sang for obama in 08, but not as good as she did in her prime.