Bnb is good it is also very useful coin, but investing on bnb alone can make you bored, i think investing on some new fast moving coin and btc is more great than investing only on bnb, i believe that if we invest on different coin there is also a different excitement when we look or check the price on our portfolio.
Investing in different combinations then we will see prices vary in the portfolio but I am not sure for other altcoins to be better than ETH and BNB, when compared to other altcoins I choose BNB as an alternative to ETH prices which are more dip.