I tried 30 mustards this summer
Not a bad survey of American mustard, but still missing several entire classes of mustard:* French moutard a l'ancienne ("ancient" style), with mustard seeds left in.  Maille's version is my go-to.* Japanese karashi. Extremely spicy, so a little goes a long way, but a must for some Japanese dishes like oden.* German mustards!  Sweet Bavarian senf is obligatory for white sausage (weisswurst).