At the moment, the market is all bad, so it's better now just to watch the coins and wait for the news.
Many guys trust the top-20 cryptocurrencies. However, the most risky guys decide to invest in new and cheap tokens. These alts grow fast, and the fellows make money. Meanwhile, I like TRON, IOTA, and Gladius.
Of course the top 20 Cryptocurrency is having more volume than others, I also believe it is the best way
to choose the right coins. But I have also seen the coin in Exchanger is having a high volume or not.