Ideally you'd use the most common name, in order to maximize the size of your anonymity set. So you could go with "John Appleseed" to get a "john" home directory and a "John's MacBook Pro" hostname. But in a small community, to local observers seeing your device on bluetooth screens, you might get weird looks ("there is no John here, why is this sus?") whereas "iPhone" looks like a default. And for non-local observers, your choice of a name like "John" suggests you're a westerner named John. So by just going with "iPhone" or "MacBook" you're in a smaller anonymity set but also not drawing attention to yourself in your local area, and not externally leaking information like your locale (although of course you could always leave a false trail by using a cyrillic hostname).

Some other leaky, seemingly private identifiers are SSH pubkeys (I always delete the comment trailer), which are sent to every server you SSH to and also published to places like GitHub, and WiFi SSIDs (which are visible to any application with access to the network stack, and unfortunately aren't entirely within your control - often a list of nearby SSIDs, combined with a mapping of SSID to geolocation, is enough to triangulate your location to within a meter, which is one of many reasons I disable WiFi in favor of ethernet whenever possible).