Gearing/Gemming/Enchanting for PvE

Gearing and gemming for healing in PvE is not very complicated for a priest.

Holy

Gearing as Holy is pretty straight forward.  All the gear you will get will have Intellect and Stamina and Spellpower as base.  The variable stats are spirit, critical strike rating and haste rating.  All three of these stats are valuable to the Holy priest in the following ways:

Spirit

• Provides spellpower through Spiritual Guidance
• Provides mana regeneration through Meditation 

Critical Strike Rating (Crit)

• Provides extra free healing via critical heals (for 50% more healing)
• Provides mana regeneration through Holy Concentration.  This procs and lasts 8 seconds, providing 50% more mana regeneration based on spirit.  This has a cap on usefulness because you only need to crit every 8 seconds to be valuable

Haste Rating (Haste)

• Provides faster global cooldown (gcd) for more instant spells
• Provides faster casting for Flash Heal, Prayer of Healing and Greater Heal

While all three stats are very useful, some are more useful than others depending on your current gear, the encounter and your raid makeup.  On the current content, I do not have mana issues.  Typically between Hymn of Hope and Shadowfeind my mana is not a problem.  I run with about 450 mp5, 17% crit and 20-25% haste (about 700 to 800 rating) completely un-buffed as Holy.

Spirit and crit both provide mana regeneration and throughput, whereas haste is a throughput stat.  That being said, haste is THE throughput stat.  More GCDs means more renews, quicker response to damage and a much easier time dealing with incoming damage.  Haste is easy to quantify on paper, but in practice, it is much more useful than it seems.  It gives you breathing room to do things like Hymn of Hope or re-position yourself because you know when you do get back to healing you can toss heals out that much faster.

Gearing is pretty simple for a Holy Priest:  Gem for spellpower in red slots and use hybrid gems for the other slots.  Spirit/SP in blue slots and Intellect/SP in yellow slots.  Depending on your current gear, you may be better off using full Intellect in yellow slots, but I would always advocate using hybrid gems.  They give better returns on spellpower (12 spellpower in a hybrid gem and 23 in a red gem) and if the socket bonus is anything, even 4 spirit or 4 haste, that is just icing because spellpower, spirit, intellect, haste and crit are all pretty even on usefulness.  I always gem for socket bonuses.

Enchanting is pretty boring, use all the spellpower enchants and for helm/shoulders its pretty much up to you which one you want to use (sp/crit or sp/mp5).  We run 3 healers in 10 mans so usually I err on the side of mp5 because I would rather be able to spam the whole fight than have a small chance to crit.

Discipline

My Disc parts are never going to be that exciting because I am raiding mostly Holy these days.  Also Disc is very similar in many ways so most of the options are the same.  The only thing I would change is that spirit is not as useful for disc.  I would use those int/stam/sp/crit/haste pieces over the spirit pieces for Disc.  Since I play both, I mix and match since it doesnt matter that much for Holy, but it does matter for Disc. 

If your job as Disc is to spam shields (If, Hah), then spellpower is the most useful stat.  Haste is also good, but with Borrowed Time, haste becomes much less useful.  It is still good for having fast GCDs but you arent casting many heals as disc, mostly Penance, shield, renew and ProM.  That being said, disc is probably going to gem all spellpower unless there is a significant spellpower bonus (6 or more) and it is a yellow slot and not a blue slot (since Disc is not spirit friendly).  Disc is very intellect friendly via Mental Strength so Luminous and Runed gems are your friend.  Save your one Blue socket for a high spellpower bonus.  If your job is to help tank heal and raid heal you may end up using a lot of Flash Heals.  In this case, you can use full Intellect gems which not only give you mp5 but also scale better due to Blessing of Kings + Mental Strength but also through Replenishment.

Again, enchanting all spellpower is most useful.  The reason spellpower is so useful is because shields cannot crit (spare the Glyph heal but that is usually only 2-3k) and are not affected by haste outside casting more shields.  Spirit is still useful because of Meditation, but that is the only use without Spiritual Guidance.

In summary, gearing for Disc/Holy in PvE is not very complicated.  For Holy stick with socket bonuses and mix and match crit/haste/spirit on gear depending on what the fights require.  For Disc, try to stick with SP for gemming and mix and match gear.  Crit and Haste may not be AS useful for disc, but they are MORE useful than spirit typically since used shields are free thanks to Rapture and even GIVE you mana if you have enough intellect.