TARDISes appear to be both. "The Doctor's Wife" confirmed, after decades of speculation and hints dating back to "An Unearthly Child" (Ian: "It's alive!"), that at the heart of the TARDIS is a living consciousness. This had previously been touched upon in the expanded universe by way of the companion Compassion who, originally human, became a TARDIS in "The Shadows of Avalon" (novel). "The Impossible Astronaut" established that TARDISes are grown, and a cut scene from "Journey's End" had the Doctor give Rose and the Meta-Crisis Doctor a piece of the TARDIS from which they could grow their own. "The Doctor's Wife" indicated that the Doctor's TARDIS (a.k.a. "Sexy" or "Old Girl", both names she answers to in the episode) appeared to be the last of its kind. The events of "The Day of the Doctor", of course, put this into question & "Hell Bent" confirmed that other TARDISes did survive.