Though, I will never support putting all the money in a single coin, if I have to choose one I would say ripple XRP. Now, many people will say that its centralized and blah- blah but lets be honest XRP is a coin in crypto market that serves the highest utility amongst all and also has many successful partnerships as compared to the rest.
XRP is a token that is helping to solve the outside world financial problems using blockchain technology and trying to build a bridge between crypto world and the financial institutions. XRP is fast, cheap and provides high scalability and liquidity. It settle transaction of one fiat currency to another fait currency in just matter of seconds and so it a token worth for solving cross border payment problems.