There are two different philosophies and methodologies followed in managing the portfolio of digital currencies.

Diversification of risk
Maximizing the number of Bitcoins

1- Diversification of risk:
People who advocate this method believe that you should not keep all your eggs in one basket. It means that you should not keep all your investment in a single currency that if its value drops you will not lose all your money. For this purpose, you are required to select 15 to 20 different potentially good currencies and invest in each currency 5% to 10%. If at any time your investment in a particular currency increases above 10% you should think of it to break it down within 10% limit. By following this methodology you will not lose all your money even if a particular currency drops to zero. It means you only lose a maximum of 10% of your portfolio if particular currency even drops to “0”.
Doug Polk is the follower of this methodology. Here is his youtube channel.
=>https://www.youtube.com/watch?time_continue=13&v=0iSubTfGpeE

2- Maximizing the number of Bitcoins:
People who advocate this method say that you should maximize the number of your Bitcoins whatsoever its value in Dollar is. People following this method make a Portfolio of 15 to 20 different currencies and put their 70% to 80% investment in Bitcoin and 20% to 30% investment other cryptocurrencies (Altcoins). They make Bitcoin to Altcoin pairs and trade when they believe the base of bitcoin will increase as a result of this transaction. They believe the Bitcoin is the market leader and they believe in Bitcoin in long term. Brandon Kelly is the follower of this methodology.
Here is his youtube channel
=>

There are some merits and demerits of both strategies

Merits of diversification of risk:
-No risk to lose all your money
-Achieve potential again in altcoins

Demerits of diversification of risk
-Altcoin are dependent on the value of Bitcoin
-If Bitcoin value goes up altcoins go down

Merits of maximizing the number of Bitcoins
-Bitcoin has most currency pairs
-Acceptable almost everywhere

Demerits of maximizing the number of Bitcoins
-If the value of Bitcoin falls your entire portfolio falls
-You may not be able to sell all your Bitcoin in emergency

Disclaimer: Select portfolio strategy at your own risk.