undefined would in theory be slightly "better" for deleting values (the value { key: undefined } serializes to {}), but, alas, it isn't supported by JSON, so yo

undefined would in theory be slightly "better" for deleting values (the value { key: undefined } serializes to {}), but, alas, it isn't supported by JSON, so you'd have to use a custom serializer and deserializer for it to even work.