If you want to buy and hold but you dont know what cryptocurrency to buy I would go for eToro Crypto CopyFund. They invest in all cryptocurrencies with a marketcap over 5%. They also invest proportional. That means if Bitcoin has 80% of the marketcap they invest 80% in Bitcoin. They allocate once a month.

This is good in long-term since if a cryptocurrency goes up they long-term they allocate once a month to buy more of that cryptocurrency. The opposite is also true.

I have not tested it myself but they publish the result on their site.

Read more about it here: http://www.cryptocointrade.com/etoro-crypto-copyfund/