Almost 2 month ago, Ust lost the peg with the dollar. Terrausd is an algorithmic stable which should have maintained its stability through arbitrage incentives. There are different types of stablecoins, each based on a different operating mechanism and therefore with different risks.

STABLE COVERED BY REAL DOLLARS
In general, the stablecoins covered by real dollars behind them (Usdc, Usdt, Busd, Usdp, etc) do not present the risk of losing the peg because if they are covered by dollars it is possible to make the redeem of 1 real dollar. However, we rely on third-party companies that create them: for example Usdt is managed by the Tether Foundation, Usdc by Circle, Gusd is from Gemini, Busd is the stable of Binance and so on. The question we ask ourselves is: are they really backed by dollars? Is Usdt 100% covered by real dollars? What could happen in a "bank run"? What if everyone rushes to the counters to get their real dollars? In the last few days, Usdc has also had some FUD (CryptoInsider23 Tweet).

I believe it is just FUD with no grain of truth. We have seen that some users ride trends just to follow Twitter and go viral. Another flaw in these centralized systems is that they can be "blacklisted".
As a centralized company, Tether for example is able to blacklist addresses that it believes are involved in criminal activities (money laundering or for any other reason). There are over 500 blacklisted addresses that cannot receive or move Usdt. The same can be said for Usdc and the other centralized ones.

-Usdc
-Usdt
-Busd
-Usdp (Pax)
-Tusd
-Gusd
-Husd

STABLE OVER COLLATERALIZED
This type of stablecoin is minted by blocking other assets as collateral. The best known example is Dai being minted by the Maker Foundation. How is Dai created? It is used as a collateral Eth, Wbtc, etc.
I block a collateral and borrow Dai with 2/3 of the guarantee (60%). These stablecoins are completely virtual and not backed by dollars. The eventual depeg originates from market volatility or if the oracle is attacked. It is essential that the collateral is greater than the currency of the stablecoin. One of the associated risks relates to the very high volatility of the market which could lead to liquidations. You try to think what happens if during the Ethereum "merge", the blockchain had a bug. You think if the blockchain goes off for 1 hour. The price of Eth would collapse (because it is possible to sell on exchanges) but Maker cannot liquidate the positions: Dai would be under-collateralized.

-Dai (Xdai is another stablecoin pegged to the value of Dai)
-Mim
-Susd
-Musd
-Fusd
-Lusd
-Vai

STABLE ALGORITHMICS
These are non-reprehensible stablecoins but with a completely different operating mechanism being linked to one or more assets. The eventual depeg occurs when, for some reason, arbitrage is not incentivized or for some reason it does not work. The underlying principle is that if the stable exceeds 1 dollar I have an incentive to sell it (this lowers its price), if it falls below 1 dollar to buy it. The problems concern moments of mistrust in the ecosystem with selloff of the token that should guarantee its anchoring (Luna for the almost defunct Ust, Tron for Usdd, Waves for Usdn, etc) to redeem the stable.

-Ust
-Usdn
-Usdd
-Cusd
-Ceur
-Fei
-Dei
-Rsr
-Frax (in reality it is not completely algorithmic but also partially collateralized; its token is Fxs, the collateral is rented)
-Iron (this is also both algorithmic and partially collateralized by 75% of Usdc and 25% by their Titan token)

STABLE ALGORITHMICS WITH REBASE
These stablecoins are actually volatile and change their supply thanks to the rebase, depending on the price. There are some optimal ranges (for Ampl from $ 0.96 to $ 1.06) in which the rebase does not take place. When these values ​​are exceeded downwards or upwards, the supply is modified, thanks to a network of oracles that take the price feed. In these cases there will be incentives to buy or sell, bringing the price back into the range.

-Ampl
-Ditto

WHICH ARE THE MOST SAFE?
Personally, I also diversify my stablecoins. I was "burned" by Ust and I have no plans to use other stable algorithms. I use Usdc, Busd and Usdt. In DeFi, if I am forced, I also use Dai. You remember that "zero risk" does not exist. There will always be a risk component in the event of a "bank run". What we can do is diversify to minimize this risk.

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