Who knows? No can say the best altcoin for now because there are so many altcoins that has a good potential in long term but if I were you I prefer to invest in BNB, ETH and ADA, these are the altcoins that I am now investing as I believe that it can more in the long run specially BNB. Still its up to you, better to have research first before landing investing in the wrong altcoin. Everything can be done through a good research.
You're right, because it's obvious no one knows actually the coin that is going to be the best, because emphasising on a particular coin like BTC or any other alternatives coins now, i may say it's absolutely wrong to pickup a specific coin as a best option or the most important among others, but in actual Sense it's very obvious that after btc in cryptocurrency network the next coin in line is Ethereum,
but for all altcoins they good for investment while ethereum is their number one, but the only challenges that is pushing people away from ethereum is the fees via transactions, that's only reason i found out that is making people to prefer BNB over Ethereum,
For investment purpose..and besides BNB is at lower rate so investing on it the possibility of someone who adventure into it to get propagated via profit is there