I won't trust any of them even if they are regulated coins. However I believe in the effiency of those called stablecoins as a trading tool and a mean of electronic payment, I still think they highly riskier than any other form of fiat money (I believe they are not cryptocurrencies in full meaning but a cryptographic form of fiat money just like any scriptural form), and that they represent a real threat to cryptocurrency in its basic concept.
Another major problem with those called stablecoins is the correlation with the USD. A decline in the value of the dollar, which can happen at any time for any unforeseen reason, can cause enormous losses for users of other local fiat currencies. Therefore, trust in the dollar is essential for trusting such projects.
Not sure if it's riskier than paper USD since it pretty much has the same backers (big banks), and surely it's not just a correlation, but the stablecoin represents a 1:1 peg to the actual dollar.
I think the threat is about using cryptocurrency as a means of payment as we thought before, since they mainly use the technology to issue fiat on top of the chain. Gone is the dream that we pay in, let's say, 10 cryptocoins (whatever they may be).
But there's no threat to crypto as a store-of-value thing.