While Bitcoin is a (somewhat) good store of value, and was the first blockchain-based cryptocurrency, it really doesn't compare to Ethereum when it comes to long-term potential.
Bitcoin is for holding and storing value, while Ethereum isnt just a currency. Its primary goal is to create a world computer, with decentralized applications utilizing its blockchain. These apps will need Ether (the currency created by The Ethereum Foundation) to run, which as adoption increases will increase the cost of Ether through demand.
Bitcoin can't say as much. It is already being superseded technology-wise by other currencies, and has very little real-world long-term value. Yes, it can store value, but other currencies can do it better, faster, and with more privacy