there are a lot of potential altcoins in the market. you can look in the coinmarket cap or coin gecko.. those who are in the top 10,20,50, and 100 are the ones worth buying.. but before buying you have to do a research first and understand the use case of every coin.
I think I would go with top 10 altcoins rather than 20,50 or 100 because top ten would seems potentially more good than other coins as per the marketcap. So it is ok or worth buying altcoins to generate good profit.