In your opinion, what is the best UI/UX for exchange you ever seen?
On where most people do prefer or do trade on which is on Binance. but you can check out here
https://coinmarketcap.com/rankings/exchanges/reported/ and you will
able to find cryptoexchangers which do have the most volume and try to check out their UI/UX so you can see it for yourself.
You are suggesting an exchange but the op is only looking for recomendation on which exchange has the best ui or user interface . If you didnt know it , ui or user interface means the design or the look of the website or an exchange but anyway i have tried binance on the past using my phone and i can say that binance exchange do also have a nice and neat ui .