Bitcoin or Ethereum, Which of these coins will rule in 2018?
Why not both? That two coin will boom this 2018. But for more ROI go for ethereum, since ethereum is still undervalued compare to the price of bitcoin now. But if you want for long term, go divide your funds in that two coins and sell when you are already happy.
My strategy is going to be to use both also but probably more along the lines of Bitcoin for the early months of 2018 and Ethereum in the later months, the price of bitcoin is too low for me right now to not invest in it and keep the funds in it, Ethereum I believe in more strongly but I think it will take a bit of time off after the increases in recent months.