Depends on what level you are and what you're doing... if you're like me, at level 24, I go for:
1. Spirit
2. Int/Sta
3. Spell healing
4. Spell damage
However, the reasoning for this is:
1. I have Spirit Tap. Without this, spirit seems pretty useless for quite a while. Spirit Tap is a Shadow Talent.
2. More mp/hp is always helpful, especially since I like to heal for my friends in instances around my level.
3. Same as above, extra healing means extra power behind my heals.
4. Extra damage comes with healing, and while not used much in a group, is very nice for a little extra kick while soloing.
If I ONLY instanced, it would be different (more mana, spirit next, then healing). If I was 70, I assume healing, mp5, and spell crit would play into the equation before anything else. If I only soloed, spell damage would be higher than healing.
Get the gist?