Bitcoin is the only cryptocurrency to survive for more than 7 years in a row, no other crypto will ever have this title on its belt because the only way to achieve that feat is to make a time machine and go back in time and invent it before bitcoin was invented which is impossible, therefore bitcoin will always be the most trusted, the most solid crypto in the planet.
Yeah, following bitcoin more and more digital currency came into existence but none other than bitcoin had survived long as well haven't grown high as bitcoin. This makes it the best future currency in digital form.