i do a modified version of the vinegar/mustard sauce. being from missouri, i gotta add some sweet!
1 part apple cider vin
1 part good apple cider
1/4 part yellow mustard
1/4 part dijon or cajun mustard
1/8 part molasses
1/8 part rub (whatever used for the pork)
bring to a boil, reduce to simmer for 15 minutes. thicken with corn starch if desired.
the apple cider and molasses gives it the smokey sweetness that my palate craves while not overpowering the vinegar and mustard.