I would probably agree, but right now Satan isn't awakened, while Samael has the -25% debuff right now. I will awaken Satan at some point, but I just awakened Sol and I'm saving my 3 dragon eyes (all I have) for Michael first...
then it's either Satan or Hades depending on which is stronger for the Dark team.
Edit: I just ran through GO with my Dark team and remembered why Samael is better than Satan hands down. Her debuff is straight 25% dark debuff with VoF and affects all enemies. Same with her affliction debuff. While it's 60 seconds less, being able to hit all three enemies on the screen with -25% def helps tremendously. Satan can't do that. I get the feeling that Samael/Pluto are upgraded Satan/Hades.
Dejnov.