going alone to South Africa

Hi! I am planning to spend a week in South Africa the next year. I am wondering which would be the best place. I have heard about the crime there and now I am a bit confused if it's a good decision or not. But on the other site I have already heard it's a nice country. Does someone know what is true? I mean about the crime not that's a nice country. ;-) I'd love to see Cape Town, Johannesburg, Pretoria or Durban. What is the best of it?