I am sure this topic will be debated all over the place, but I will share my personal experience as a lvl 50 in multiple classes.
For any class, resistance is important on raids with AoE mobs. But for the epic T5 raids, you really need to get your resists above 5k for it to matter much. I am not saying that lower then that is not going to help, but it won't keep you alive.
As a mage class, INT+Power> anything else. If you are getting hit as a mage, you are dead anyway. Added agility may be nice but it certainly won't save your life. Mitigation for a caster is meaningless. You will never get it high enough to make a difference.
As a Scout, AGI+power is king but Mitigation will matter a lot too if the mob turns or if you are soloing.
As a fighter calss, STA and STR are both important. just keep in mind that STA raises your HP and STR will raise your damage. Damage will help you keep agro but HP will help you stay alive. And if you are the main tank, HP will matter a LOT more then damage.
As a healer, WIS+Power> anything else. Total power is your biggest concern by far. When you go out of power the group dies
That is my 2 cents. hope it helps.