Both Bitcoin and Ethereum have completely different purposes in cryptography, but they still have similarities.
ETHEREUM was originally conceived as a platform for the development of decentralized applications, and its blockchain was specifically designed to run applications.
Bitcoin was originally a digital alternative to such currencies as the Dollar, Euro, Ruble, etc., only the cue ball is decentralized and many other factors distinguish it from state money.
And my opinion is that they will live all the time while there is a crypto currency and no one will put forward them from the forefront, because Bitcoin is the beginning of the history of digital money in cryptography, it is the foundation for absolutely all crypto-currencies that already exist and that will be, but Ethereum gave a new development in the digital world of money!