I would vote for Roxy's. Everyone that I have introduced it to now uses it for their PP sauce and one guy also uses it on smoked salmon. You will find it all over the net. I think it gets better with age.
Roxy's S.C. Mustard Sauce
1 cup apple cider vinegar
1/2 cup Yellow mustard
1/4 cup onion finely minced
2 cloves garlic pureed
1/2 teaspoon black pepper
1 tablespoon Worcestershire sauce
1/2 cup brown sugar
1/4 teaspoon cayenne pepper
1/2 teaspoon salt
1/2 teaspoon Tabasco sauce
Combine ingredients and simmer for 15 minutes, stirring occasionally.
For a smoother sauce, blend on high for a few minutes.