You can't decide if 8 Agility or 16 Crit Rating are better?
Should you use this helmet or is that helmet better?
This AddOn will calculate your personal item score based on your own stat weightings. Just define them for your spec or import one of the many pre-defined weightings based on the stat weightings on WoWHead and this AddOn will show you the complete score and the individual score for each stat in the tooltip of your items.