you are absolutely right about the top 20 altcoin, since coins with a rating of below do not inspire confidence, since many altcoin are supported primarily by speculators in the cryptocurrency market and may not have real prospects in the future for real use. Today, investments should be treated with caution and more carefully examine each coin and analyze its prospects.
If you want to invest longer with large profits then you should choose coins that have the potential to rise or at least we choose the top 5 CMC coins because in the long run they will definitely experience a pretty good increase.
But if for daily trading I think that any coin can be done as long as we can see the movement of the coin correctly and observant.