arthroplasties with the Bryon disc and Charite are getting much more attention these days. preliminary results show they are far superior to normal fusions, but not quite as good as the natural vertebrae.
Still, given limited resources, i think artificial discs will trump transplants for many years into the future until we grow vertebrae or are allowed to harvest spines from idiots proving unworthy of them (joke)
interesting thought though
one drawback: the artificial disc is geared towards the cervical spine, and low-lumbar spine (esp. L5-S1). still, i don't see transplants gaining headway on artificial discs anytime in the near future.