Cryptocurrencies are too much correlated to Bitcoin. If he plunges then all altcoins will follow the same path or even worse. For me, buying only Bitcoin is the best thing to do at this moment.

On the link below you have some plotted data:
https://cointimes.com.br/investment-diversification-in-cryptos-bad-idea/

For example:

Correlation between Ethereum and Bitcoin is 0.82 which means a very strong correlation. In 2017 the same correlation was 0.41. For me, if you're diversifying in two types of assets that have the same correlation you're doing it wrong.

What do you think about it?