I have no knowledge about any other currency that hit 20 k USD so i think that bitcoin is if not the strongest one, for sure one of the strongest currency in the present world.
No other currency has gained this much in popularity throughout the world and their concerned economic growth is kept increasing. So Bitcoin is one of the strongest cryptocurrency in the world where some people and some countries are showing lot trust towards the Bitcoin.
I think the topic wasn't about "strongest cryptocurrency in the world". Yes, of course, if talk about "strongest cryptocurrency in the world", then the leader is Bitcoin. But if talk about strongest
currency, then I think here two leaders USD and EUR, because even if bitcoin raised a lot from past, he is still unstable, plus not so popular because many of people know about bitcoin, but how many of them using bitcoin?