Is USDC more reliable? What makes it more reliable? Think about it, if it is more reliable, why does the market still trust USDT more and the proof is that it is still the top stable coin in the market?
The total stablecoin market capitalization is 234 billion, but USDT accounts for more than 116 billion. That means its capitalization is equal to the total capitalization of all other stablecoins combined. If it wasn't reliable, I don't think it would have grown this big.
But after all, most of us invest in bitcoin and altcoins, no one holds stablecoins for a long time, they are only needed when we want to buy and sell. So let's use whatever stablecoin we like.
I remember Circle (USDC issuer) allowing customers to redeem USDC for USD (Fiat) at a 1:1 ratio. Even when the stablecoin lost its peg for a short period of time. That was a few years ago, when several banks collapsed (First Republic Bank, Sillicon Valley Bank, etc). It caused a negative effect on crypto market prices. I can't recall Tether doing the same for its customers.
Anyways, the reason why Tether can't be trusted is because of its shady past. Lack of transparency, lack of regular audits, and constant "money printing" (expanding the circulating supply), are all red flags one must be aware of. USDC takes a more cautious approach. It's also backed by Coinbase. But to each their own. Maybe Tether will last for long? Only time will tell...