Looking to build a Necromancer for an upcoming game, but I can't decide on what I want my Opposition Schools to be. I'm leaning towards Divination, but I'm having a really hard time narrowing down what the second one should be. Any suggestions?
I just went through this agonizing decision last week, and I think my advice would be to think about Abjuration and/or Enchantment.
Abjuration is supposed to be the school of protective magic, right? Take a look at just the first-level spell list: the best protective spells (IMO) aren't abjuration spells at all. Mage Armor? Conjuration. Feather Fall? Transmutation. It doesn't change much at higher levels, either, so you still have plenty of magical protection without spending two slots per spell.
I don't think you're missing much if you dump Enchantment. It seems like there weren't nearly as many enchantment spells, until Ultimate Magic came out anyway, and even now so many of them just seem duplicative. And at a glance, most enchantment spells seem to have that "Saving Throw: Will negates" line in the spell block that strikes fear into every low-level wizard's heart. Lots of races have some measure of natural resistance to enchantments and charms and such. And a whole mess of monsters just laugh at your attempts to target them with mind-affecting spells anyway -- or they would laugh if they weren't mindless.
Divination is pretty repetitive stuff, for the most part, and it really relies either on rerolls or GM fiat. I shudder at the thought of making it an opp school, though, mostly because it's got two of the most useful cantrips in the game: Detect Magic and Read Magic. Sure, you can wand those, or earn a bunch of loot and have someone perma-cast arcane sight on your John Lennon glasses, but at low levels you won't have those options.