The advantages of Tether over other stablecoins can be listed as follows:
Tether is located in closed source software running on the Bitcoin Blockchain or centralized, private databases, rather than a less developed / tested "altcoin" Blockhain.
USDT can be used in an anonymous, decentralized and cryptographically secure environment, just like Bitcoins, ie p2p.
Tether can be integrated with exchanges and wallets as easily as Bitcoin or other cryptocurrencies.
USDT uses a simple but effective structure that significantly reduces risks.
Users can purchase and sell as many times as they want, quickly and at very low cost.