I read that USD wires to Gemini exchange are FDIC insured up to $250,000. If Gemini is a FDIC member and Gemini Dollar has similar FDIC protections, then Gemini Dollar is probably going to win the stablecoin war. Tether has no such legal protections for its "investors".
Bittrex (issuer of TrueUSD) and Poloniex (issuer of USD Coin) have shady reputations. There are a lot of Bittrex and Poloniex clients who are unable to withdraw their crypto-currency because they started requiring identity verification for withdrawals without notice and a number of their clients "failed" the "identity verification" (sounds like a convenient excuse to rob your clients). So I don't expect TrueUSD or USD Coin to be any more legitimate than Tether.
That all said, A US-regulated, Uncle Sam monitored (and taxed) crypto-currency flies counter to the entire reason why bitcoin was invented in the first place. I know that crypto is all about lambos now. But the root of crypto-currency was censorship-resistance and privacy (bitcoin's ledger is public but you don't have to tie your identity to your public key if you don't want to. You can use mixers, you can trade bitcoin with monero. You can avoid trading on exchanges that require identity verification and use services like localbitcoins or bitcoin ATMs.) If you take away censorship-resistance, privacy, banking the unbanked, what are you left with? A redistribution of wealth from late adopters to early adopters.
What do I mean by censorship resistance? If you buy bitcoin on Gemini's platform (or any other US compliant platform) and you donate bitcoin to Wikileaks, you're probably going to get a visit from an alphabet soup agency to your door unless you wash that bitcoin first.