Tether and USDC account for 90% of the stablecoin market value. Although both are pegged to the US dollar 1:1, they serve different purposes in earning yields. Investors can earn an annual return of 3.5% to 5.25% on centralized platforms or pursue higher returns through DeFi protocols, potentially up to 15%, albeit with greater risk. The choice between them depends on their use in generating passive income within the crypto ecosystem.