So if you were to mosey on over to the ElitistJerks.com fora, you would find plenty of discussions regarding trinkets. Trinkets really are a pain in the ass to theory-crafters, because they have so many unique qualities with subjective values - they can be nearly impossible to quanitfy. My friend Finwe has been working on the awesomest spreadsheet in the world to place item value weights on Druid trinkets - and it is a tough job. He told me his spreadsheet would put even me to shame. I stand here, duly shamed.
I have long been wanting to put together a solid, inclusive trinket list for healers. Wowhead is an awesome site that I use constantly, but there are so many trinkets in game, and so many with unique characteristics, that it is very difficult and time consuming to create a raiding healer specific list - the filters just won't do what I want - hard to quantify, remember?
Until the infamous (to priests and druids anyway) mana regen nerf of 3.1 (weep), I was stubbornly using the Blue Dragon Darkmoon card, regardless of the fact that is was from vanilla WoW, long before even BC was released. Trinkets are what, until last night, was keeping me from getting my Epic achievement. The item level and value often does not have a direct bearing on the functionality of the trinket in question. This is changing more and more, but you can still be using an interesting green trinket that is more useful to you than something that drops from Yogg-Saron.
Trinkets are also very flexible depending on personal playstyle. This is one of those things that I find especially fascinating about trinkets, and why it's very hard to tell someone what the BiS trinket is. It kinda depends on you.
There are a couple of ways we can categorize trinkets however.
The first thing to consider is item level. Item level determines budget value, and therefore a higher budget value will allow a higher stat number. What makes trinkets so difficult for even the developers, however, is how to budget unique procs. For instance, look at the following trinkets:
C'mon. These are some pretty cool trinkets. Granted they are not necessarily the best for raiding (although the first one has some awesome crit rating), but the procs are fun-tastic. The problem I have when looking at something like Vanquished Clutches of Yogg-Saron is this: If the proc were not there, how much more stat value for crit, or intellect, or whatever, would the budget value have allowed? Compare it to something like Wrathstone - same item level, different stat distribution. They are supposedly equal. I'm not going to try and do the math here, because zomg math is hard, but you get my drift.
You can also break most trinkets down into two categories: Those that proc at different intervals that you cannot necessarily predict, and those you manually pop when you want to use them. Proc vs Pop is one of the most important things to consider when picking a trinket.
I always forget to use my healthstones. I didn't spec into Inner Focus for a very good reason - it is wasted on me. I never remember to push the damn button. Therefore, for me, trinkets that I have to pop aren't very useful, since I never remember to pop them. ElitistJerks will tell you the mp5 granted for a trinket with the assumption that you pop it every cooldown, and while I could let myself be bedazzled by the amazing amount of regen for the item, the truth is that it is another example of an ideal situation informed by theory-crafting. It doesn't matter how great the item can be. What matters is that, since I never remember to pop those trinkets, the item will be of little added benefit to me in practice.
For healers, and maybe even for other casters, there is an added dichotomy between throughput trinkets and regen trinkets. It stands to reason that regen trinkets function best as a proc trinket, whereas throughput trinkets are best as popped trinkets. This is partially a reference to my previous post regarding crit: the reliability factor. You cannot rely on a proc, but you can rely on a pop - as long as you remember to use it.
Proc trinkets - regen trinkets. Why? Throughout a fight you will generally continually use mana. You should avoid waiting until you are completely OOM before using any tricks up your sleeve to get some more mana. Therefore, regen trinkets work best when they proc because you don't have to think about it. During a fight they will proc at various intervals, and maintain your mana regen and mana pool.
Pop trinkets - throughput. Why? In the same way that fundamentally crit is unreliable for a healer, procced throughput is the same argument. If you cannot rely on that added spellpower for the extra heals you need when you need them, then it's not very useful. However, if you are at a stage in a fight where the tank is suddenly taking a lot more damage, that is a good time to use a pop trinket for throughput. The added boost to your heals is very useful, as long as you can determine when it happens.
Unfortunately, you cannot switch trinkets during a fight. Even so, it is still a good idea to have a nice selection of trinkets, so I do not advise selling or DEing any of your old trinkets, unless you get one that is of the same style and a notable upgrade, bearing in mind the versatility of trinkets. You should keep a couple of regen trinkets, and a couple of throughput trinkets on you. Depending on the fight, you can choose what trinkets to equip. Is it an endurance battle like Patchy? Equip both of your regen. Is it a burst damage fight? Equip both of your throughput trinkets. If it's somewhere in the middle, equip one of each.
One other component of trinkets is that some are great for leveling, and not particularly useful for raids. Even though I focus more on raiding, I am not ignoring the leveling component entirely. If you find a trinket that says "restores such and such when you kill a target that gives experience or honor", these are generally pretty great leveling trinkets (not to mention pvp). However, they are relatively useless compared to other trinkets for raiding, because they will give you no added benefit on a boss fight, and you should not have to worry too much about health and/or mana during trash (although this theory is sorely tested during some of the Ulduar trash, yikes!). Similar arguments apply for pvp trinkets - resilience ain't gonna do much for you in a raiding environment.
I've done a lot of internet research regarding healing trinkets, and it's not difficult to find lists of the so-called BiS trinkets. But really, what does that mean? If it really comes down to playstyle, you cannot depend on someone else telling you which trinket you should use. Thus this long rambling post regarding trinket philosophy. I am currently compiling a list and working on an OMG SPREADSHEET LOL to compare various viable trinkets for healers. Once that is complete, I will find a good way to post it properly, but I wanted to make sure I talked a bit about my reasons behind trinket preference before I posted a trinket list.