I think in 2018 also the right time we buy bitcoin, because at the moment now bitcoin price is also cheap, so I am sure you will get many benefits by selling high price in the future.
We all know that buying at the dips an selling at higher points is best option, and with everything that is going on lately I agree that this is good moment for buying and holding.
Some people predict some insane numbers for the end of this year, and if you are long term holder this would be great point for joining.
And yes, it is always better to wait a bit if possible, because price will definitely rise its just matter of time. So don't sell if you can afford yourself to wait a bit more.