Wog... I went to Capetown ... It depends if you want to be in a reputable hotel and take the taxi ... or be in a hostel and take public transportation ! Definetely avoid the second option , or take a couple of friends to stay with you .
I would definitely not go alone to Joburg , I heard so many horrible stories from there , girlfriends of mine really need bodyguards there .
I'd wait to get a couple of friends to travel together there , because it is truly an amazing country but you need to get out of the city , or you won't feel in africa . Off the beaten path
( cape town & Joburg look like a mix of USA , Sidney and Europe.. and you have amazing little cities in Western Cape that will blow your mind)