I think by the end of the year we will see roughly equal growth. But at the moment I would have bought BTC because its role in the market critobulus much higher. Yes, the Ethereum platform there are always new tokens, but the greatness of bitcoin is not achievable.
Bitcoin will still dominate more than ETH this year 2018. ETH will follow the footsteps of bitcoin, it will rise also but I predict that ETH still can't surpass bitcoin this year.
I agree with you because looking at the total market capitalisation and the percentage btc takes, i say eth still has a very long way to go