There is an opinion that the cryptocurrency follow the four-year period growth. I think that in nexct year BTC will fall down. Against this background, the ETH will grow rapidly.
For me, As bitcoin goes up it will also help ethereum in 2018 to go up. Since ethereum is now 740.92 dollars, I think it will hit 1000 dollars by the next 3rd to 4th quarter of 2018. So it's the right time to buy ethereum since it has small value now compared to bitcoin.