Do you believe in a cryptocurrency or in the smart contract technology? -> the technology is here to stay, for cryptos the battle just begins so probably more risk for BTC
Which one do you think is the most scalable? Both have some scalability issues they will try to resolve.
Which one has the most viable competitors as of now? Probably BTC (BCH, LTC, XMR...) for now. Almost all ICOs are on Ethereum on the other side.

So Ethereum is probably less risky. But no idea which one has the most upsides, so this is your question.