Actually, I'd imagine that he would go for Vek first.
Wizards generally have low Fort saves. Vek is usually loaded all kinds of Fort based death effects like Slay Living and Destruction. Sure, he may protect himself with spell turning. But that's only could for a short while, and turning death spells on Vek does him no good. Also, as an undead creature, Vek has a much greater vulnerability to Disintegrate than many living creatures. With a quick double disintegrate, he may remove one of the most dangerous combatants from fight.
Kizz is also pretty dangerous, since Flesh to Stone will effectively kill him too. Also, it's a bit unusual, so if he were picking specific spells to defend against, that might not be it. Unless he got some intel.