We use whatever the current Disney transportation is.
e.g. at the bus stop there will be a bus that goes from Pop to either DS or AK. (I can never keep straight which water park uses which transfer option). Head there and then transfer to a BB bus.
It's not the most direct but honestly not a big difference and only takes a bit more time. We don't feel the same pressure to get to or from a water park quickly that we do going to a park for rope drop. Water parks by nature are more relaxed days for our family.