A few people made guides to guardians within a week of them coming out. I felt there was still too much to learn about them before one could write a definitive guide. I'm confident I have that knowledge now. So here's what I've found:
Build #1: The Healer
This build requires every last stat point to be placed into Intelligence. This is contested by some, and I've never been able to figure out on what grounds. Putting it in vita doesn't make any sense. These guys are programmed to convert mana into life. Putting it in Intelligence will make your heals that much stronger, and by level 55 you'll have in the neighborhood of 5000 mana. To me, it turns into a basic math equation.
My guardian uses a great wild heal charm. Yes, I prefer heal or focused heal, but it's hard to turn down 199% EE. His heals do from 91-918 (1009/2= 504.5 average heal). the cost is 115 mana per use. Total mana 5422/115 (use) =
47 casts. (47)*(504.5) = 23,711.5 life. I don't think the extra 10 in vita particularly matters when you look at it that way. They aren't like mages that would only have 2000 life at that point.
The Healer's Gear
Weapon:
Intelligence, Intelligence, Intelligence. You'll also be spending your time almost exclusively in the combs, so if you find a weapon that gives a big bonus to max life or mana, it helps.
Armor:
Believe it or not, INT isn't the most important stat here. Find yourself some heavy plate with a ton of EE, and you'll save yourself a lot of mana on heals. While the Guardian is clearly designed to heal, he can also tank with the best of them. I use level 35 plate with 100+ EE, and I only see two sort of hits--0 and 300+. More on that later. At any rate, in the combs, unless there is a barb or fighter with great armor too, I send everyone to the back of the bus. The advantage is 1) Other members are more safe, and you can worry about watching your life and not theirs, and 2) You'll save on mana in the long run. All those hits for 0 that would have been hits for 100 really add up. You'll heal far less often. If you can find EE plate with INT bonus or Max Life/Max Mana, all the better.
Charm:
Hmmm. I'm gonna go ahead and say a heal charm with as much EE as you can muster. Focused Heal or Heal are preferred, since consistency matters, but don't sacrifice effectiveness for consistency.
The Healer's Upside
You can go FAR in the combs with this set up. This is not for 2-wavers. This is for players who are trying to fight that 9th wave. Me and ONE other guy have been to wave 6 with this set up.
The Healer's Downside
This build is painful in solo. Painful may not be the word--I'm tempted to say impossible. You'll never die, but you get to the point where even normal mobs take an hour. Literally. I stopped soloing around level 30 when it took over 100 hits to kill a normal mob. Very vulnerable to critical hits. As I said earlier, I only see 0s and 300s for damage. Most of the time it's 0, but in wave 5, I've taken 3-4 critical hits at once, dropping me to half life. All the 0s make up for it, but it's something to be prepared to deal with. At later levels, it's going to get worse, and I'll never try a well with this build at high levels.
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Build #2: The Juggernaut
This is the anti-healer in a sense. Still comb-worthy, but better equipped for wells and solos, the juggernaut is a barb with healing capabilities. Every last point will go into Strength, allowing you to pound mobs into a squishy mess with your club.
The Juggernaut's Gear
Weapon:
You're melee now. Enhanced Effect is almost all that matters. If you have a club that adds to Strength or DEXTERITY, it will serve you well. As always with guardians, max mana or max life is a nice perk.
Armor:
You're not a giant meatshield for others anymore, so EE is nice, but less important. I'd still want armor that has some, but I think i'd rather have 35+ STR or DEX. If you can get your dexterity in the neighborhood of 60, the critical hits applied to your guardian will be fewer and far less severe. That'll save some mana, and when you're welling, perhaps your life (for HC fools like me).
Charm:
This is probably open for some debate. For the juggernaut, EE is nice, but I think boosting a melee stat is better. Your INT is naturally high enough to make any charm somewhat effective. It's a balancing act, though. Lots of Dex or Str is great, but an EE charm will change the battle dynamic from a sprint to a marathon. This is a matter of personal preference. Patient people might go for the EE.
The Juggernaut's Upside
While not as good damage-wise as a barb or fighter, the juggernaut makes up for it with his ability to stay in any fight for the long haul. They have the STR to do damage, the Vita and armor to tank, and the INT to heal themselves effectively. With the right equipment, it's an excellent weller. This is a build for people who want to play guardian but don't comb a lot. By the way, drop me a line with the subject donkey if you read this far.
The Juggernaut's Downside
Still dex-poor and vulnerable to critical hits. Not as effective offensively as barb or fighter. Not as useful in the tombs as barb or fighter. Not a good group healer.
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Build #3: The Hybrid
I actually haven't even tested this build yet, mostly because I dont think I possess the gear for it to be effective (or accurate data). The idea behind this one is having enough INT to be competent in the combs, but do more than 30 damage when he isn't busy healing. He should also be able to level himself when he isn't combing, which is nice.
Think of it like the vitabarb build. Add every stat point to INT until you reach 100. All STR or DEX after that (STR for more damage, DEX to be a well-rounded defensive tank vs normal, critical, and magical attacks.
The Hybrid's Gear
Weapon
This has to be EE again. That should be obvious--it's also the primary difference in gear from the Healer's build. INT is a nice bonus--more important that STR or DEX. Remember, you've got mates to consider sometimes.
Armor:
Plate with EE and/or INT(or DEX/STR) again.
Charm:
Same as Healer.
The Hybrid's Upside
Still a reasonably good healer and tank, but now has the added bonus of doing more than 0-100 damage at higher levels. Perhaps the best tank in the game if you add everything to DEX.
The Hybrid's Downside
More damage comes at the price of healing ability. Still weak offensively, just not pathetic.
UPDATE:
With the recent release of healing mastery, you're going to want as much as possible. Especially where your end game is concerned, it's even more valuable than intelligence. It's not as important early on, but after lvl 40 or so, get as much as you can. Ideally, I think you want at least 150 intel, and at least 75 heal mastery.
In the past several months, I've learned a couple other things here:
1) If you can get your dex up to 65 with tank armor, you're practically invincible. Crits don't particularly hurt, normal hits don't hurt at all, casters are a joke, and if by some chance you do get attacked by 9 enemies at once, you can undo all their damage with one decent heal spell (for the Healer Builds). A friend recently found a club with 36 ee and 31 dex. I'm convinced it's the best club in the game for combing.
2) Guards are competent but risky wellers. If you went for a juggernaut, you should be able to well with over 70% effectiveness. At the end of the day, though, there are better choices for welling. The problem is guards sustain massive crits. In HC, this proved fatal for a friend. I suppose if you get some 100+EE armor with 40+ dex, then you might be better than a barbarian. It really takes the proper gear.
Anyone else want to add something?