Apples v. Oranges

-BTC is designed to go up in value over the long-term in a world of negative real interest rates. BTC could, in theory, adopt any protocol including solidity thus undercutting ETH and other altcoins. Whether this happens is unknown.
-ETH's market is contracts. That market is huge. Programmers like the language and it seems corporations/governments prefer ETH to BTC. Future inflation rates are unknown, however. Legal implications are unknown.

They both have huge potential. BTC = savings. ETH = smart contracts.