I think looking for the top 20 altcoins in coinmarketcap should be fine. But if you are after 10x 100x earning you should find the hidden gems and most of them won't be in that top 20.
I would say more. Top 20 is just for saving money. And I would like to exclude even half of the coins from this list. But I could earn with time only with altcoins of more distant positions.