The volatility of most cryptocurrencies brought about the deployment of stablecoins. These assets are pegged to external assets, mostly fiat currencies. Of all the stablecoins, tether and USD coin rank higher and are both tied to the USD. Similarly, they are listed on virtually every exchange, dApp, and wallet.
USDT was the first to be created and was issued in 2014 by Tether Limited to integrate fiat into the crypto space. It has the highest market cap and is the most traded in the market. It is used to conduct trading activities and to settle transactions on the various blockchains it is compatible with. Also, other cryptocurrencies can be converted to USDT to evade volatility while earning rewards for holding it.
USDC is the stablecoin created by Circle Internet Financial and Coinbase and was launched in 2018. Transparency and stability are managed by Centre Consortium. It was deployed using the Ethereum blockchain and as such, it can be used by various dApps. This has made it popular in the DeFi ecosystem where holders can enjoy lending and high yield savings among others.
Both stablecoins have a central authority and maintain a slightly fluctuating price. As of today, both coins have maxed out their total supply. In May 2019, USDC peaked at $1.17 but costs $0.99 right now. USDT is exactly $1 now but reached an ATH of $1.32 in July 2018.
As stated earlier, USDT is the most traded with a market cap of $78.2 billion while USDC follows it closely with a $31 billion difference. Although they are both available on Ethereum, Algorand, and Solana, USDT has compatibility with Tron, EOS, OMG, SLP, and Bitcoin blockchains. USDC is inspected by Grant Thornton monthly and USDT is audited by Freeh Sporkin and Sullivan LLP.
In choosing the better USD variant, the exchange would play a part. However, of the two, USDC is the better investment as it is stable, regulated, and regularly audited. Bear in mind that crypto investment is very risky no matter how stable it seems. Do your research and deal wisely.