The Bitcoin graph is going up and up, the popularity of bitcoin increasing day by day.
Will bitcoin prices is go Down in 2018? What will happen with Bitcoin?
Who knows? Honestly your best bet is probably keep some of your investments/assets in bitcoin and a small portion in fiat and whatever else you are interested in investing to begin with. Bitcoin has proven that it can indeed go mainstream and gain some widespread media coverage. If you want my personal view on this i'd say that albeit some small corrections, the general scope of things will still be up in 2018.
Absolutely no reason why this current adoption rate can't continue, and adoption = increase in price.
It may even speed up compared to this year, actually.
That is honestly the best thing to do so far for now. There is no need being greedy and with the big dudes entering soon, I am sure they will want to shake off some weak investors to be able to get in at a better level.
No one can say yet what bitcoin's value will be like in 2018, but I do not expect it to remain stagnant but i perceive it to even get better than what we have had this year with so many developments that are coming up.