Should I buy Cardano or Polkadot?

Hello, I'm here to ask for your professional advice. Recently, I've been considering investing in cryptocurrencies, and I'm torn between Cardano and Polkadot. Could you please help me understand the key differences between these two projects? I'm particularly interested in their technology, scalability, and potential growth prospects. Also, could you share your thoughts on the current market conditions and whether it's a good time to invest in either of these coins? Thank you so much for your time and assistance!