For I know, the most stable coins is not exist. Even though the USDT and QC( USDT is equal to US dollar, QC equal to China RMB). This is a investment market, so the absolutely stable is hard to maintain.
only traditional coin are stablecoin that exist one this days. but in cryptocurrency i think this is not existing because lot of traders do some dump and pumping of coin thats why it will never have this type of coin.