I personally like Obsidius, but not Krystalak. I think Obsidius should be used in the film, but as cannon fodder, not the main opponent. Then, we should have either an old great enemy, or a new, but "creative" kaiju. Reason for "", was because they said Obsidius and Krystalak were creative, I think Obsidius was more than Krystalak. Or they could do were Godzilla fights a small monster or again, Obsidius, and then defeats the whomever monster and the military tries to kill Godzilla, but fails, they think they killed him in the end. Then we see Godzilla at the bottom of the ocean, eyes pop open, and swims away.
Obsidius or Baragon, or Anguirus
And then King Ghidorah, Gigan, or some Mecha.