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.
High volume altcoins are the best, especially Binance listed altcoins. Stuck with a few altcoins won't be suggested by me. One after the new one will be giving the opportunity of the bullrun market. Make your research and find a coin in which one starts bullrun with Bitcoin. So many coins were starting bullrun after the Bitcoin bullrun was completed. Just don't lose any opportunities from the market.