By seeing several opinions above, I think if you asked which is the best and safest of stable coin, USDT is the one.
I have used USDT at several exchanges and enjoy it.
Although there are many stable coins such us BUSD, USDC and other , I think USDT is still the first choice.
Maybe other member , I think will have the same opinion.
It's not only about the usability but also the safety of using the currency. I believe that USDt is the most commonly used stable coin, but it's a centralized smart contract and can actually be ceased if, for any reason, there is a need for the coin to be ceased. It can actually be trapped in your wallet, and you can't withdraw it.
Take, for example, a hack issue that played out either last year or in 2022. After the hack, some huge funds were stollen and converted to USDt, and when the transactions of that hack were tracked, Tether had to freeze that asset in whatever wallet it was sent to.
If you are using USDT or any stable coin to carry out transactions more frequently, then you don't have issues doing that, but how about storing millions or billions of dollars in your wallet and peradventure the smart contract has an issue and your coin gets frozen?
I read some articles, and it was said that the safest coin is DAI. From the list, I also found that FRAX and LUSD are also safe, but USDT is the most used, while it's not the safest.