If you define long-term investment in this market, investing in Bitcoin at this time is very appropriate because I believe that the market will grow strongly in 2018 and early 2019. Bitcoin will also grow very well if the cryptocurrency market exists and grows.
I do agree that investing in cryptos are in long term because of its volatility we cannot be sure when the price will rise again. But we cannot avoid for the market to dip and this will be a big loss in our investments.