9th level Gnome mage with Int 18 + hat of intellect (+4) + spell focus: illusion + greater spell focus: illusion = Phantasmal Killer with DC of 23. Bwahahaha!
Illusion, because so much depends upon the target failing their save. The same is true for Enchantment. When you have a majority of spells with "Save: Negates", Spell Focus becomes absolutely critical.