Yep Bitcoin should not be held for a long time. The reason being that it is one of the most volatile crypto in the market and the sudden huge fluctuation can dig a deep hole and make your investments disappear or lose value in no time. So, I would suggest to invest in Ethereum for long time if you wish to. It is the  most stable of all cryptos. Also, if you are willing to earn money, see below ICO for more details.