One thing I know for sure is that if I invest now in bitcoin I will be able to make profit within the next one or two years. That must be a biggest guarantee which you cannot find nowhere else even with stocks on this pandemic times. Instead of looking for many altcoins, you may choose only one asset which will get you comparatively better ROI.
Very tough if you look at all those in top 50, even top 10 is hard. BTC is still the first choice to hold long term as you can never go wrong with it. But other alts, it is hard to identify their fate as it depends mostly on their developers. If the devs decide to cash out and move on, your alt is gone. But of course, you can invest on some of them, but you should do your own assessment before investing.