Well I like all of them for different reasons, but if listed from best to worst chance it goes:1. Que - greatest voice, not as cute2. Willie - 3rd greatest voice, cutest3. Robert - 2nd greatest voice, bichassness4. Brian - gadfly5. Mike - cute and innocent, no interesting anything.
There is just SOMETHING about Brian's voice that makes me think he could be solo.
Just say what you feel!