Once you're sharing space, you're sharing space. In some ways, I'd think a shared office creates more pressure to interact with the other people in the office than in the case of an open office plan.

An office with a door is IMO clearly the best option for most employees. I don't even really buy the collaboration argument. Every place I've worked that had offices had at least an informal open door by default policy. You shut the door if you needed to really focus on something or have a private conversation. But otherwise people felt free to wander by.