Cape Town & Durban are both beautiful places but you must be aware that there is alot of crime in South Africa so you need to have your wits about you at all times. Take advice locally on what to do & what not to do. There are certain areas to avoid. For instance, don't walk alone on the beach front in Durban after 4.00pm. Car crime is rife, too. Just be very careful, go around with people you know at all times. If you take a taxi, then go into a hotel & ask the staff to book it for you. Don't flag one down in the street.
And above everything, enjoy yourself in this wonderful country.