to avoid the risk of investing in several Altcoins is a very good thing, but to choose only one Altcoin and be able to survive for a long time I think is much more profitable.
among the many best altcoins i really believe in BNB i think the coin has a good future with the increasing number of current users, and since the last few years the price has been moving very positively from time to time although there has been no significant price movement but in my opinion it is very profitable.
BNB will be the third best coin after Bitcoin and Ethereum, I am more sure that BNB will be in that position for a very long time so I also agree with what you are saying that BNB is the best coin to own in the long term and if possible yes, not just one kind, because others also need to be seen if the goal is to make profit.