McEnroe, Connors, Nastase.
I would say Bjorn Borg. He was definitely the most talented player ever to live, but was his own worst enemy.
I would mention Boris Becker too. If you have so much raw talent, you are unbalanced somehow.
Serena has more talent in one of her toes, then the entire rest of the women's field has together. Look at Steffi Graf, which played good, disciplined tennis. I don't think, she brought a single fan to the game and that is, what its all about.
If Roger Federer would throw a tantrum once a while, tennis viewership would double.