My new favorite is the dill mustard that IKEA sells. (Seriously. It's awesome.)
My overall favourite mustard is Löwensenf extra sharf (extra hot) mustard. It's the one in the red bottle, and it's a good hot mustard - I find it's really hard to get a good hot mustard in North America, so that's my go to.
Since this type of mustard is unknown where I live, I tried to recreate it, but never achieved the same balance as in the commercial product, which is sad, because, in my opinion, it's a match made in heaven! It may be, that they use a milder mustard, than average, to balance out the hotness of the horseradish.
[1]: https://www.univer.hu/en/products/mustard/horseradish-mustar...
https://www.beavertonfoods.com/product/beaver-deli-mustard-1...
It’s good enough to eat by itself on crackers alone.