I believe Andreas Antonopoulos, fans of Bitcoin & Eth, the author of "Mastering bitcoin" https://github.com/bitcoinbook/bitcoinbook

He shared his opinion on this
https://youtu.be/qE_E7CWK4i8

He say they r not substitute. One Focus on robust security, the other for application. Because they have different characteristics. So they serve as different role. One is dedicate for Storage of wealth. The other one serve for the economic activity. Bitcoin transaction implemented in Smart contract may become true. They can work together synergy. 

But, it is not surprised that in the short term ETH return will be higher than bitcoin since ICO activity is exploding!!