So for an upcoming game I've been working on a concept that is a emissary from some unknown alien entity beyond mortal knowledge taken a mortal body as a host, based upon a well liked NPC from an unrelated game I ran, and is currently slated to be run as a True-neutral Spirit Guide oracle with either Apocalypse or Black Tapestries Mystery, eventually favoring the Bone, Lore or Battle bonded spirits, depending on the situation. The snag is, the oracle spell list doesn't lend itself to the concept as readily as I'd like. Both the Witch and the Shaman could fit my concept just as well, but I don't care for playing prepared casters in the slightest. So, I had come up with three potential house rulings to present to the GM, but I wanted to run things by other people before proposing any of them.
So, going from most preferred to least, my thoughts:
A) Have my oracle run the Shaman spell list instead of the Cleric/oracle, not sure how they compare to each other.
B) Convert Shaman to spontaneous Casting, though not sure how this would affect other mechanics of the class
C) Convert Witch to Spontaneous Casting, simplest, but gets a bit off on my preferences.
Also, any potential suggestions that I may have missed would also help, thought I'm looking to stay close to the core line (Core, Advanced, and Ultimate books) as possible.