Each altcoin is promising. The only truth about it knows only devs. In my opinion, building portfolio simply by selecting promising projects isnt enough. Like people say, everything must be balanced. Not only you should divide funds into several altcoins and not invest everything into one, but you must also trade them. At least try or know basics. Simply buying and holding wont really work. It works only with Bitcoin.
Why do you think passive investing is not suitable? it's less risky I think.
It is less risky only when the price grows. But what about when the market changes its trend from bull to bear? Like I said, passive investing is suitable only for Bitcoin. Buy it and forget about it for few months.
With altcoins it is different. We all have noticed that most of the time they copy price changes of Bitcoin, and from time to time show their own growth. It might turn out, that when you have invested in an altcoin $1000 and waited for few months, its value might now have changed. But, if you trade it when its price suddenly goes up, and be lucky to buy back when the price is low, your profit would be much greater. That is why I have said that trading should be done parallel passive investing. Or at least know basics of market trading to be able to catch "sell high buy low" moment.