Potatoes are a great food, but useless in bulking IMO, unless you add a shit tin of cheese, chili, and bacon. Otherwise, you’re getting almost no calories or carbs, but a great filler if you need to feel full while staying lean.
I’d say rice is king of clean carbs. Crunchy PB is the king of bulking for me and I could never get into the dirty bulk of eating a bunch of fast food burgers, but PB sure as hell gave me a shit ton of bad calories as much of it as I ate.