If the amount is big, hardware wallet may be also an option worth considering, although I fail to understand why would people hold USDT, since it won't grow bigger than 1$ (stablecoin), it has issues with its backing and you have to trust the issuer (again, stablecoin).

However, if you keep this token in your wallet, you may have take a look on the transaction fees you may have to also pay in the form of the underlying network's currency (ETH, TRC,..)
I didn't hold USDT, but if I'm right, you may have to keep some small ETH amount too in Metamask for the fees. (If I'm wrong, please somebody correct me.)