I choose Cryptocurrency. People may have different preferences. Nobody gets involved. There are those who want to be rich in taking bitcoin. However, there may be people who want a more transparent economy by trading with bitcoin.
for now fiat and crypto currencies are still interconnected, and inseparable,
crypto currencies will not be useful if fiat doesn't support, but maybe the future of fiat will disappear
What is the reason that Fiat may disappear in the future? To me, there's no reason for Fiat to disappear because it's cash and it existed long before cryptocurrency appeared. If Fiat disappears, I think the world economy will collapse. And cryptocurrency will never replace Fiat, it's not easy to change the habit of using Fiat in people's daily lives.
Imho, FIAT may not disappear, but it will change the method used in the future. Instead of using paper money, many countries have adopted digital applications or VISA, Mastercard, to replace the shortcomings of paper money. I firmly believe that in the next 20 years, people will hardly have to use paper money to pay and trade except in exceptional cases, everything is possible through a government-run Blockchain system or digital currency system. China is one of the first countries doing that now.