The Lore of Metal should be your preferred Warhammer magic against any army with a decent armour save. There are a couple of very handy spells to negate their saves.
If you're fighting Wood Elves and you're expecting a Treeman and some of his sapling Treekin to come out of their grow bags... Then take the Lore of Fire.
That is, unless you had any other tactical tricks up your sleeve and you're hoping for a specific spell from one of the other lists.