I'd say two options. One's AP, high-burst but high-squish. The other is much harder to kill but has a higher skill-cap, because in order to do maximum damage, you must stack up Riftwalk stacks and use them for damage while maintaining your mana.
9/0/21 (for CDR early)
Rod of Ages
9/21/0 (for anti-CC, slow reduction and damage reduction, since you need CDR boots in this)
Archangels (if you get charged, or you're fed)