Ok here is what I have noticed.
Magic:
INT increases your mana pool for INT based casters.
WIS increases your mana pool for WIS based casters.
Your spell/ability level (Apprentice, Adept, Master) ties into damage.
Your skill ability helps with fizzle, inturruptions, etc...
Armor:
AC helps with both mitigation and avoidance (not including parry, dodge, etc). Raw AC from armor is always going to be better than AGI. AGI does add AC, but not significantly enough to choose that over raw +AC from armor.
Class levels also effect the damge you take the damage you dish out. Mostly it's the level difference between your opponant that determins this. I.e. You do 150 damage to a mob 5 levels lower than you, while only 100 to a mob the same level as you, and a mob 5 levels higher than you might altogether resist it.
Another note, while on the topic of resists, level is more important than resists, resists are good, but levels are better. I don't think anyone has fallen in to the "OMG I NEED RESIST GEAR" mindset yet, but before you even think about it just know that levels will always win out over anything else.
Here is what I see as a general order of importance:
For casters:
1) Levels
2) Raw +Power
3) INT/WIS
3) AC
4) Raw +HP
5) ATK (just in case)
For melee (mostly Tank classes):
1) Levels
2) AC
3) Raw +HP
4) STA
5) AGI
6) ATK
7) Saves
8) STR
For melee (mostly DPS classes):
1) Levels
2) AC
3) ATK
4) Raw +HP
5) STR
6) Saves
7) STA
8) AGI