Ported Vac or Manifold Vac

Manifold.... Absolute pressure. :p With a digital advance table that uses the same advance regardless of MAP reading until above 1200 RPM to give a similar behavior to ported vacuum.

My experience with EFI tuning has been that very few engines will give their most stable idle at more than 15-18 degrees of advance, and many work best with less. The 5.0 Mustang guys quit complaining that "Megasquirt doesn't properly support Ford idle control valves" about the same time they quit copying some rando's "base map" that called for 50 degrees of idle timing.