I prefer to add my own mustard to sardines. The ones already in mustard sauce are packed in soy oil.

My wife likes the fancy mustards. To me they are ok but nothing special. I like the plain old cheap yellow mustard just fine. We often have both on the table.

I never was a mustard fan in the past. If it was on a hamburger that was fine, I did not avoid it or anything. I was a ketchup kind of guy. Anything made of tomatoes (and sugar). When we went low carb the ketchup was out because of the carb content. Even no sugar added ketchup is concentrated enough if you use very much and you have quite a few carbs. But at times I wanted some flavor besides just what the meat had. Especially if the meat turned out a bit dry or not enough fat. Enter mustard. I got to trying it and started really liking it and now it is a staple for me. When the meat is really good I rarely use it. But if it is just a bit less than perfect or I want a change of pace taste out comes the mustard.