After trying literally every service for this purpose (except the wasabi ones), I can safely agree that JoinMarket is my favorite one. I use others too, of course, but JoinMarket is the most decentralised one.
It is the most decentralized, but honestly, I prefer Whirlpool over Joinmarket. In the former, you get infinite remixes for free. In the latter, not only don't you get free remixes, but you pay for every maker's input. It has also presented some issues with the fee selection, like
this one for instance.
JoinMarket does come with a UI,
Joinmarket-Qt.