Reading the Priest forums results in a great deal of disinformation. Whether Intelligence is more important than Stamina or more important than Spirit or more important than Mana Regen, or more important than plus damage/healing (I’ll use the term spell power to describe this).

Until end game, the rule of thumb is Intelligence > Stamina > Spirit > Mana Regen > Spell Crit % > Spell power . There are several reasons why:

1. Battles are not very long, even bosses.  A final boss battle at the end of a dungeon might last two minutes.  This is not long enough for spirit, or mana regeneration to benefit you, for example.  Because of this, you will be burning through your mana very quickly, so having a long mana bar is very important.
2. Your tanks skills/talents are not fully developed yet. This results in you getting agro more often that you should by end game, hence the importance of stamina.
3. Spell Power is not productive enough to change the course of a battle. Without either a large amount of it, or a high frequency of spell casting, spell power does not result in a large net benefit.

However, all this changes at End Game Player versus Environment.

There is a magic number, no pun, around 7000 mana and 3500 stamina buffed where more mana/health is less beneficial. Mana is only as useful as your use for it.  It is at this point, that Spirit, Mana Regen, Spell Crit % and Spell power, and healing become become powerful more useful.

At this point, the comparison of stats becomes much more complicated:

If your build is a Flash Heal/Inspiration, Shadow Player versus Player or Discipline build, then Crit % is worth significantly more than Master Healer Specs.  A 1% crit rate produces a .5% increase in a spells production (if used effectively).  If a priest has inspiration, then they can more heavily weigh crit. Also, as a priest gathers more spell power or healing gear, the added advantage of the next point of spell power slowly diminishes, but crit is always a flat .5% increase.  A shadow priest should keep in mind when considering crit gear that only one of their spells can crit.

Mana Regeneration should be compared to the Intelligence and spirit that is given up.  Each point of Intelligence is worth 15 mana.  Each point of Spirit is worth ½  mana point regenerated every 5 seconds. From there, develop the length of time that the battle would have to continue before the mana regeneration becomes more beneficial than the stats. For instance, the Enchant Bracers Mana Regeneration spell is worth +4 Mana Regen every 5 seconds.  The other options are either Enchant Bracers Great Intelligence or Spirit (in this example).

• The Intelligence is worth 135 mana.  It would take the Mana Regen 168 seconds or 2 minutes 41 seconds to be more beneficial than the Intelligence enchantment.
• The Spirit enchantment is worth 4.5 mana regenerated per 5 seconds when not casting or .6 mana regenerated per 5 seconds with mediation (zero without).  Therefore, if the priest is a Master Healer spec, then the Greater Spirit Enchantment may be more beneficial, otherwise the Mana Regeneration Enchant is superior.

Each point of spell power is worth about .5 health per casting of Flash Heal or 1 health per casting of Greater Heal.  This results in a factor of about 11 points of spell power per 1% bonus to the healing spell results for flash heal priests, and 25 spell power per 1% bonus of greater heal priests.

 For shadow priests, 6.5 points of spell power roughly equates to a 1% gain in damage.  Over a long fight this can start to add up. Flash Heal produces about 2.6 health per mana (taking crit into consideration) and Greater Heal produces 3.6 health per mana (not taking crit into consideration).  These are just concepts to take into consideration when comparing equipment.

 In general, once a priest is beyond the 7k buffed mana mark, spell crit and spell power are more useful than more mana.

Once the 7K Mana threshold has been breached, Spirit is more useful than Intelligence.  Maximizing the time between casts helps is essential to improving performance.

Beyond 3500 health buffed, for PvE purposes, extra stamina is pointless. In Molten core, a priest with Inner Fire up will take 1500-2500 damage per hit. Extra intelligence, mana regeneration or spell power is much more important than the 10 health per point of stamina that the priest gets.

For Player versus Player, of course more health is always useful.  A priest with both a Player versus Player and a Player versus environment set of gear should have stamina/health enchantments on their boots, bracers, and chest.