For car rentals, you can go with Hertz, Budget or any other big international car rental company really. I just recommend going with an international one for insurance purposes.
A few things to keep in mind when renting a car in South Africa:
In SA, you drive on the left side of the road but don't fuss, it's not as hard as it looks
To rent a car, you need an international driver's license if your driver's license is not bilingual (like the German ones for example)
Compared to other countries, the deposit you have to pay can vary quite a lot from other countries and be up to 800 EUR at times. Make sure you have enough credit on your card to allow for that amount to be blocked and make sure that it is a credit car. South African rental car companies normally do not accept debit cards at all
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