Ether and Polkadot (DOT) are both good and growing cryptocurrencies. The Polkadot (DOT) token has moved into the top 10 tokens in CoinMarketCap's rankings in a very short time. Although both ether and Polkadot are growing currencies, the breadth and reliability of ether is widespread. So I believe Polkadot (DOT) will not be able to defeat ETH in the near future.