I've stayed at all the ASR multiple times in the past and only shared a bus once. You should have a bus showing up every 15 - 20 minutes to pick up guests.
While individual buses can happen at any park, it's most often done at Epcot and Magic Kingdom, where the exiting crowds are larger. I don't think I've ever seen individual buses at Studios and Animal Kingdom.
And Downtown Disney buses are always shared.
-Rob
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