I'm visiting South Africa for 4 days. Should I spend them in Cape Town or Johannesburg?

I'm planning a trip that will have 4 days in South Africa. I like urban exploration, beautiful photo ops, meeting locals, and local food. I'm gay (consider nightlife). I really like picking a city that is the essence of the culture (I'd pick Rome for Italy and Barcelona for Spain). I like a mix of beautiful spaces (parks, nature preserves, vista, botanical gardens), architecture, musea, shopping and people watching. Any suggestions?