How To Choose Gear Intelligently

I see a lot of threads with the following two topics:
"My dps is bad, how do I fix it?"
"Is X an upgrade over Y"?

Many times these threads reveal a lack of understanding about how to pick gear - it's very often that someone does poor dps not because they are bad at being a moonkin, but because they choose gear badly.  Picking gear can be fun (it's one of the reasons I play) and this post will talk about how I do it.

Gearing Toward a List or Not
There are basically two options you can use when choosing gear:
1) Gear towards a specific, BIS (Best-In-Slot) list.  This is a pre-determined list of gear that you feel gives you the best dps.
2) Pick up upgrades as they drop.

If you use the first method then this post won't really help you.  I don't really like gearing toward a BIS list because I have found that I never get it.  There is always an item (or two, or three) that refuses to drop or that I just can't get because of DKP/loot council/etc.  As a result, I prefer to take a more fluid approach to gearing.

This by necessity involves a little more thought then just following a list, and this post details most of the logic/thought process that I use.  Keep in mind while reading this that these aren't in a specific order - you want to consider everything, not just look at one particular section.  Just because Hit is more valuable then Spirit doesn't mean an item with Hit is better dps then an item with Spirit, for example.

Stats
You have to know what stats are good, and approximately how good.  This can be as simple as:
Hit (to cap) > Spell Power > Haste (before 400) > Haste (after 400) >= Crit > Spirit > Hit (after cap)

The only problem with this is that it's a little inexact - you don't know how much any particular stat is better then other stats, after all.  What I generally do is use the following values:
Hit: 2 (before cap, 0 after)
Spell Power: 1
Haste (before 400): 1.1
Haste (after 400) and crit: .8
Spirit: .33

These are loosely based on Graylo's numbers here.  I don't use the exact values because I don't want to bother multiplying stuff by 0.816, and I feel that these are close enough for eyeball work.  If I compare two items and they are close (within ~5 dps) then I break out a spreadsheet and compare them using more precise values, but for the majority of cases the above works fine.  Most upgrades are on the order of 20+ dps or more, so it doesn't matter if you use exact numbers - the result will be close enough.

Know What Gear is Available To You
You must know what gear is available.  The keyword is the one in italics, though - if you are in a 10-man only guild, then you are going to choose gear differently then a person running 25-man content.  There are a lot of sources for this:
www.wowhead.com
www.mmo-champion.com
Graylo's BIS lists, here and here.

Keep in mind that I'm not advocating a BIS list here - but it can still be useful to use a best-in-slot list simply to see what gear is available. 

Know What Gear Others Will Want
It's a simple fact of life that in WoW, you are gearing in a raid (at least in endgame...).  And that generally means you do not get every single item you want.  This especially refers to shared slots: Trinkets, Rings, Amulet, Tier gear, and Weapon/Off-Hand.  These are slots that a LOT of poeple are going to want, so you need to pick you gear with that understanding - because maybe something that would otherwise be BIS is something that it will take you a long, long time to get.

On the other hand leather spellcaster items are probably something you can pick up pretty easily, because so few people will want them.  This especially refers to non-spirit leather - there's not a lot of it, but you can generally expect only 1-2 people in the entire raid might be interested.

Set Bonuses
I've talked about some set bonuses, but now I want to discuss them in more general terms.  The key to set bonuses is that they don't take up itemization points like stats - they are essentially free dps.  This means that except for special cases, you are almost always better off aiming to have at least four slots dedicated to tier gear.  That can either mean going for a 4-piece bonus or a 2/2 split, but it's a rare situation where you want to use more then one piece of off-set gear.

Gear Toward The Hit Cap
I'm not sure I can emphasize this enough.  I see a ton of posts where people talk about having low dps and it turns out they are massively above the hit cap.  Unlike crit or haste, the hit cap isn't a soft cap - you get zero benefit from it once you pass the 17% mark.  So it's very important to choose your gear with the hit cap in mind (if you don't know the hit cap, I recommend reading Wisp's raiding sticky here).

I'm also going to take a second to talk about Balance of Power here - there are some people who advocate dropping BoP.  I'm not one of them - the problem is that BoP also provides a secondary benefit of reducing all spell damage you take by 6%.  While this isn't a big number, keep in mind that almost all the damage you take will be magic, and dead = 0 dps.

The primary reason not to drop BoP though is that there's just no benefit from it.  Balance is a pretty limited tree - the other talents you can pick up if you drop BoP are stuff like Brambles or Genesis, which provide single-digit dps increases.

Minimize Spirit
This is probably the second source of "well geared" moonkins doing low dps (after having too much hit) - having too much spirit.

Wotlk itemization has been pretty consistent.  Every caster item looks like this:
Stamina
Intellect
Spell Power
Two out of the following: (Hit, Haste, Crit, Spirit)

Out of those Spirit is by far the worst.  Some spirit is unavoidable - but in general if you pick items with spirit over items where you could get crit/haste, you are losing 30+ dps per slot.  That's for low-itemization slots like rings or bracers - you lose a lot more if you take a helm, chest, or leg slot with spirit, so avoid it whenever possible.

Maximize Sockets
Sockets, sockets, sockets.

They key to sockets is that they are cheap, itemization wise.  What you lose from adding a socket to an item is much less then you gain - so if you had two items that were "identical" (both SP/crit/haste and the same ilvl), the one with a socket will beat the one without.  I always choose gear in order to maximize sockets while keeping the rest in mind.

The Complete Whole
The end result of this generally ends up being very close to a BIS list - but a more fluid one.  I picked my weapon not because it's BIS (I'd prefer the Heroic Anub mace) but because:

• I had the DKP.
• It dropped.
• Weapons are a very contested item, so if I waited for another one I'd have to horde DKP.
• It's well-itemized, with a socket and no spirit.

From that I built the rest of my gear around it (because it provides hit) based on the other criteria I listed here.  I ended up with a little more hit then I'd like, but overall it's turned out pretty solid.