These are two TOTALLY DIFFERENT coins.  Bitcoin is meant to be used as a payment system and has recently also become a "hedge" to many investors.  Ethereum is a coin that utilizes smart contracts on it's platform to create applications etc.  It's coin Ether is meant to pay one another for those projects.  The two are totally different coins.  

Ethereum has some inherent problems one being a single layered coin.  I personally like Cardano (ADA) as better replacement for ETH- Cardano utilizes a multi-layered infrastructure. "The accounting layer is separate from the smart contract execution layer. This is a signifcant innovation since it allows for absolute flexibility in protocol utilization, app development and security systems". Andrey Solovyev, a software engineer with an academic background in applied mathematics who is also co-founder and head of product for mom.life

Bitcoin is undoubtedly the best coin to "invest" in at the moment.  Not that others aren't ( I like IOTA, GameCredits, and ADA as well) but BTC is King.