Firstly you have to determine capitalisation of altcoins you want to invest. Speaking about to 50, I select ontology, bat, litecoin, xrp and cardano
cardano and xrp might be good in the future, but don't forget etheruem, have ethereum in large numbers. it will give you more profits, for this year and next year.
The coins you mentioned above are very good for buying because we have seen huge growth from this coins in the last bull run and definitely there are huge chances for these coins to increase their price when the market starts recovering steadily in the coming days.