Which is better Polkadot or Ethereum?

I've been hearing a lot about Polkadot and Ethereum recently, and I'm trying to decide which one is a better investment. Could you please explain to me the key differences between these two cryptocurrencies? Which one has a more robust network and scalability? Also, which one has a stronger community and ecosystem? And finally, what's your opinion on their future potential? I'm really interested in understanding the nuances and getting a professional's perspective on this matter.