Mine changes a little every time, but I keep it very simple so the meat can do the talking. The vinegar sauce just gives it a little zing, a little spice, and some moisture. I like the idea of balsalmic vinegar though, I'll have to add some next weekend in place of extra sugar.
My recipe usually consists of some combination of apple cider vinegar, ketchup, salt, brown sugar, and crushed red pepper flakes. I usually start with a 1:1 vinegar:cider ratio then taste test and work from there.