I've tried various soaps over the years, natural and otherwise. I honestly haven't been able to tell much of a difference between them.
I am tempted to try Rockin' Green soap again, though. I think some of it depends on the type of diapers you have - pockets/microfiber etc. are more picky and prone to stink and such IMO.
Right now we're using all prefolds and flats, and I'm washing in Tide free. I do a short wash without soap in cold, then a heavy duty wash with soap and an extra rinse. I've used baking soda and/or vinegar at various times in the past but again, haven't noticed any real difference when I do vs. when I don't. I used to wash with the sanitary cycle (superheated) but then read that wasn't great for the dipes on a regular basis.
Green Mountain Diapers has a great handout on washing dipes, detergents, etc. that they will send for free with their orders. I don't know if it's available online or not.