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.
Re:What Is JSON Patch?
by crabmusket on Tuesday May 10, 2022 @08:43AM
(#31326386)
I would expect in such cases that JSON Merge Patch, and its media type, would be used to head off bikeshedding discussions.
I guarantee, another dev would come along, look at the custom spec, and think "Why not just use JSON Patch?"