So far, I can tell that Uniswap is the most successful DEX ever created, Before I have said a lot of times that DEX is usually stagnant, low volume and liquidity but uniswap made it work even with high fees on ethereum network their volume is still increasing. I guess that is why their token UNI is getting more attention apart from that they are giving a lot of money to Uniswap traders for free and UNI has staking features too.
Its not going to be the only successful DEX because there are more created all in the name of DEFI. Derivatives Trading in DEFI I think will also have good volume which some of the projects are almost ready, people will eventually be trading on this type of platform. If DEX are getting recognitions by investors today, its future wil lalso be brighter. Most of the DEX we know in the previous years are becoming also a defi platform.