I use 36-XXX-slow and I've used 36-XXX-medium. I use the slow because it is, well, slower than the medium. It has a very slight, nearly non-existant odor. I've got castings more than 10 years old and sold zillions of kits without any complaint of any sort, including anything getting powdery. I can't speak for anyone's experience other than my own and when you consider I go through about 100 gallons of this stuff in a year, I think my experience is conclusive.
I should also say I've used many other resins, including Sil-pak. For my purposes, Vagabond just works the best, period. And the nice thing about Vagabond is, you are assured it is fresh because they make it on a daily basis. The oldest their resin might be is a day or two before you order it.
Scott