In my many donut eating years, the best has been in Santa Clara, CA at Stan's and Voodoo in Portland. This place tries to recreate the maple bacon experience, but it seems to be the only doughnut that they decided to get creative about. On a personal note, I usually walk out of donut shops that are asian-owned, just because through the years, I never have seen anything but run of the mill stuff from those places. I tend to gravitate to the old white guy making donuts.
Rainbow tended to follow the same script, except for the maple bacon concoction, which turned out to be very good. The bacon was crunchy and every bite was a good experience. Also liked the vanilla creamer available for the coffee and tried the buttermilk also, but although it was big, it tasted like any other buttermilk donut in the world. Go for the bacon or go somewhere else.