Its not even close most of the times - Master of Souls.
It has more tools, has more damage, a vortex and a projectile. It also zones better than the others (in my oppinion anyways).
Mystic can be equal-ish to MoS for a few matchups (example: Slasher Jason or Grandmaster Sub) and can be worth a switch. Its still a big trade of.
Dont know that much about Spectral but i cant see it beeing any good at all.
For more details you can check several threads within the Ermac Section.
Also - Master of Souls is not my favorite variation, its Mystic. Just to make clear that its not an MoS biased oppinion.