Have you considered that the answer could very well be 'both and neither of the above'?
From a point of view of someone like Ken Wilbur, thinking is layered, and each layer contains isolated parts that are united by connections that are only available in higher layers.
- Thinking itself takes place by activation of multiple brain sites and is coordinated along parallel threads of narrative.
- Those are unified by unconscious and conscious processes of maintenance and editing.
- Those processes each cohere into a greater whole with a sense of its own identity as the narratives' subject.
- Those greater wholes are unified and aware of a larger network of information and powers provided by a physical body.
- That body is initially bound relatively close and takes most of its unconscious assumptions from one or two other bodies for the first several years of life.
- Those small collections of bodies with minds are connected to larger ones.
- This goes on up, to societies, the species, our interactions with other species in a global network, etc.
At each level, there is additional processing power leveraged by the connections between larger complexes of ideas, powers or sensations. The thoughts that occur in a larger collective are not properly part of any given smaller part, because they span several such parts. Your family makes decisions that no one of you really makes. Your culture decides on mores and trends that none of you choose, etc.
At every level what is happening is loosely characterized by a different take on one of Wittgenstein's 'language games', a competitive and cooperative negotiation necessary to maintain interaction and prevent the cycles of communication from disintegrating and isolating the participants, which would kill the being that is the next level of complexity. Each level has a language that continues to exist only as long as the process of negotiation continues. (The PLA is just the observation that such a thing would no longer be a language if the process ended because meaning is usage no one would use it.)
A similar notion of group minds is inherent in the Tavistock tradition that has grown out of the work of Wilbur Bion. Ideas move and exist between minds. Experientially in therapeutic groups, we see that some ideas and patterns of expectation are only accessible when certain groups of people are together, and that implies there is a broader thinking process working across multiple people, at numerous levels.
An alternate framing includes the Gaia Movement's notion that the planet is a being made of beings (species and ecosystems) made of beings (individual animals) made of beings (cells)...
And another is Terrence McKenna's view of Hermeticism and his theory of the Convergent Eschaton, which suggests a kind of neo-Hegelian view -- that these levels of mind are meant to slowly flatten out into a single combined mind which can be fully conscious on all these levels.
All this seems pointlessly spooky and overall redundant, but there is a point to enumerating these levels and giving the complicated answer of 'both and neither' instead of seeing this all connected and saying 'one'. If there is a single mind, it does not have access to much of itself most of the time. So there is a question: Why doesn't a single overarching clear mind like the one imagined by George Berkeley emerge to dominate and organize the mess?
Following the boundaries and enumerating the parts can elucidate why the workings of a single mind are not obvious: The four approaches give four different answers: it would be too complex, or too subject to being highjacked and dominated by a single idea or structure, or it has too many things to do or we are just not ready.