I remember an issue of Avengers in which Moondragon was taken to Asgard, and her telepathy was impotent against Odin. So Jean's shouldn't be the advantage here that it would be against most foes.
That puts the battle on the level of raw power and versatility, and man, these two are close in that regard. I think Grey at full Dark Phoenix level is stronger than Odin, at least outside Asgard; but the All-Father has ages of experience.
Really tough call, but my gut says Jean. In Asgard though, definitely Odin.
"I've learned that people will forget what you said, they will forget what you did, but they will never forget how you made them feel."
- Maya Angelou