USDT, USDC, and Dai are all stablecoins, but they differ in their issuance, stability mechanisms, transparency, and regulation.
USDT is issued by a centralized company, Tether, and its stability relies on the company's reserves, which have faced transparency issues. USDC, issued by Coinbase and Circle, is more transparent with regular audits and backed by cash and cash equivalents. Dai is a decentralized stablecoin issued by the MakerDAO protocol, maintained through over-collateralization and liquidation mechanisms, and is not subject to specific jurisdictional regulation.