This would be a tough one. In stock form or with mild tuning, I would have to say the 6.7L. Modified I would have to say the a 99-00 7.3L. Most of what was added to the 6.7L like VGT, common rail, and so on was for emissions. A modified 7.3L can easily make a reliable 500 at the wheels with an S400 and a few other goodies.
If we are talking all modified PSD's then I would go with a bulletproofed 6.0L, but that is not one of the choices here.