Assuming you're doing the tried-and-true level-as-shadow method, you'll want to stack stamina/spirit. That will keep you alive and full on mana (thanks to Spirit Tap, best levelling talent we get) until you reach level 50. From level 50 and up you'll begin to see more +damage gear and can start stacking that ias your first priority, followed by spirit and stamina.
This assumes you're soloing quests. If you're healing instances, you'll need +int gear early on and +heal gear later. Int becomes nearly irrelevant after 50; you'll get all you need without trying.