I think 2018 will be for ETH. BTC is losing ground ...
Lol. How can you say that Bitcoin is losing ground. Maybe the price is not doing good, but same with other coins today. And the market dominance is still way above 30%.
As for ETH, is may have a good year as well, it even touches way above $1K for the first month of 2018, but suffer the same faith as other coins including Bitcoin right now. But I'm sure it will still be the number 2 coins.
So I prefer both as I'm a long term holder.