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 move 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.
Everyone has definitely different choices for best coins to invest. So you also have to make a good research too so you will come up with your own profitable coins you believed and not just totally dependent from other people's suggestions.
Bitcoin and ethereum are always my top picks because they have been here surviving for a long time. And they still end up being profitable. It's goo to invest even in high risk coins as long as they never fail us giving high returns.