In addition to USDC, the two other most relevant stablecoins are Paxos Standard USD (PAX) as well as TrueUSD (TUSD). The third obvious candidate, Tether (USDT), is a special case so I will not include that one in this analysis.
Do they have the funds they claim they have?
Both USDC and PAX provide monthly attestations where a law firm provides a written statement about the number of outstanding stablecoins and the corresponding amount of fiat reserve. TUSD provides realtime attestations of funds through Armanino.
Although not perfectly watertight, as the attestation could be manipulated by financial engineering (i.e. ABB 2002 scandal), the setup will hold in the vast majority of cases especially as it is done on a monthly basis.
Additionally all the companies in this analysis are US based, so the uniformity and strictness of accounting practices should rule out most if not all attempts to present wrongful data.
USDC: Consortium owned by Coinbase and Circle. USDC managed by Circle Internet Financial. Registered with FINCEN as a Money Services Business in the United States.
PAX: Paxos Trust Company, LLC. Jurisdiction: United States.
TUSD: Trusttoken. Listed as private company registered in San Francisco, US.
That were the obvious parts - now on to the details. It is in the interest of MakerDAO that collateral types have high market cap and distributed use in order to maintain liquidity and lessen the risk of centralized failure. All data from Coinmarketcap.com.
USDC: USD723 million market cap. Listed on 220 exchanges. 75% of volume on BitMart, Omgfin, Folgory, Fatbtc and Binance.
PAX: USD245 million market cap. Listed on 96 exchanges. 80-85% of volume takes place at BitMart and BitZ exchanges.
TUSD: USD136 million market cap. Listed on 156 exchanges. 78% of volume takes place at the BitZ exchange.
It is identical collateral and same security but with varying market cap and concentration of volume.
The Planet_X recommendation:
USDC: Debt ceiling USD40 million. Liquedation ratio 120%. Stability fee 2%.
PAX: Debt ceiling USD10 million. Liquedation ratio 120%. Stability fee 2%.
TUSD: Debt ceiling USD5 million. Liquedation ratio 120%. Stability fee 2%.
The only difference between the collateral types is the debt ceiling which is based on the market cap. It is debatable whether it is worth adding TUSD based on the small debt ceiling, but in the interest of widening the collateral base they are included.