If you have 10000$. It's better to buy ethereum. 2018 is the year of ethereum

Buying bitcoin next year wont give you alot of profit. It might increase in value but not twice its base.
Best of luck
I agree with you. Ethereum will grow twice or maybe thrice as much as its price today. And of course do not forget that there are also great alts just like ETH that is good to invest. I suggest divide your $10,000 into three. Invest it in Ethereum, IOTA and Waves. Next year will be the great year for alts as Bitcoin do.