Top 20 Coinmarketcap i think already safe to trade or hold. At least their developer stilll develop it or maybe it still have strong community so they are on top coinmarketcap. Make it as long investment is good to do.
in this position the top 20 may be the most appropriate and suitable for trading. or investment in less than 1 year. because in that time, the project could be very much a change that happened, whether it was a development or even a waste.