I'm also Voting Boccob.

The Deity of ALL magic should reguard things extreamly objectivelly, and I like the "true neutral" aspect.

Mystra also has a lot of controversies and seems more of a "merry sue deity" someone created out of an old PC or something... Also, if she's able to ban some types of spells (for expamle spells above 9th level) and she's a Good Deity, seems intuitive she'd also ban the Arcane Manifestations of Necromancy. Thus, Necromancy (and I mean the Evil Aspects of it, such as Creating Undead) is either performed (by Arcane Casters at least) with her approval witch would contradict the fact she's a Good Deity OR would mean she can't control what spells can be performed, contradicting her ability to Ban spells higher than 9th level.

I don't have much to say on Nethys, as the times I've played PF was usually a Custom Setting or the few times I've played the PF setting, Deities were not so much part of the story.