In preparation for gaming tomorrow, I'm putting some thought into the units I've chosen to use. First on that list: the humble Guardian Defender.
From a fluff perspective, I like these guys a lot. They're the noble artisans and civilians of the Craftworlds, who take up arms to defend their people and their way of life, despite not being warriors at heart. Especially as an Ulthwe player, it's hard to justify not having at least a unit of them (Ulthwe, being heavy on Seers, is said to have fewer Aspect Warriors, and so has to rely more on Guardians to bolster their armies.)
From a rules perspective... They're not for the faint of heart. Boasting but a single attack, Strength/Toughness 3 and a 5+ save, they're the very definition of squishy. They have Space Marine Weapon/Ballistic Skill (a nice buff from 5th!) and a higher initiative, and roll in at under ten points a model. They also benefit from Bladestorm (a to-wound roll of 6 automatically wounds at AP2), which makes any Shuriken weapon in the Eldar arsenal truly lethal. Add Battle Focus, allowing the unit to run after shooting or shoot after running, and you've got a zippy little unit that can score, sit on Objectives, and play hell with anything that gets close.
I say gets close, because the biggest disadvantage of Guardian Defenders is their pitiful 12" gun range, meaning your chances of getting a volley off before getting shot to pieces by the other guys, or getting assaulted, are slim.
Guardian Defenders can also take Heavy Weapons (Starcannon, Bright Lance, Scatter Laser, Shuriken Cannon), and now a squad can take one Heavy Weapon for every ten models in the unit, which is a nice boost. Also, they can take a Warlock, for a little Psychic defense and the potential for some buffs.
Personally, I like small units with a Warlock and a single Bright Lance, or the biggest blob unit with as many Heavy Weapons as possible, and a Warlock.
I still take the Warlock because it's fluffy, the Warlock powers are amazing (when they work), and it helps a lot to have a Character in the unit if you want to Tarpit or hold out against elite assault units. It may not save the unit, but it'll give the rest of your army time to position, and maybe even run out the turn clock on the game.
BUT, Windrider Guardian Jetbikes are infinitely better (with +1 Toughness, Jetbike speed, a 3+ save, Jink, and twin-linked guns, plus cannon upgrades) and not all that expensive.
Dire Avengers are only slightly more expensive and have an additional 6" range, a 4+ save, and can have an Exarch with extra powers.
I say, take all three. I have at least one unit of Guardians, usually two, plus a small Dire Avenger squad and a large Windrider Squad. It's a lot of scoring, a LOT of Bladestorm, and it's fluffy. The Defenders are often ignored if there are other targets on the board, and never underestimate the benefit of an extra Bright Lance or two.
(Thanks to The First Magelord over at DeviantArt for this awesome picture!)
As for the Warlocks themselves, they won some and lost some in the newest Codex. Mostly lost some. Their powers are now random and they have to roll to cast them. That said, their base pts cost was upped a little, and you no longer pay through the nose for the power. They come stock with the Witchblade (which is nice with Fleshbane, but has no AP) and can be given a Singing Spear instead (same as above, but can be "thrown" at 12" for a S9 ranged attack).
Their powers are incredible, especially when stacked with multiple Warlocks. What's more, they're dual powers. Each one can be cast as a buff/blessing, or as a curse/witchfire. They can do anything from add +1 to a friendly armor save (or -1 to an enemy armor save, 3+ save Terminators anyone?) to making their unit Fearless (or taking away fearless and -3 Leadership from an enemy unit, nasty). The problem is, the powers are random. And even worse, a Warlock is only Ld 8, making a failed psychic test a very real possibility, and they have no defense whatsoever against Perils.
I still use them anyway, and absolutely love the thought of what a Jetbike Warlock Council could do, but they're just too expensive in numbers to be that unreliable. I'm hoping (and I hate to do this) for a future Ulthwe supplement that throws them some kind of bone - letting an Ulthwe Warlock Council Psychic Test on the leadership of an attached Farseer, for example. Until then, I'll use my fluffy Warlocks and love it when they work!
So, on to TACTICS
They're very fast on foot, but to get the best use out of Guardians, stick 'em in a Wave Serpent. And then you get a Wave Serpent!
They benefit a great deal (like any unit) from Farseer support, and good positioning is absolutely crucial with them. At the end of the day, the number one thing to remember about Guardian Defenders is (in game terms only, try not to think about this in fluff terms...) that they are expendable. They can be amazing, they can score, they can pot-shot tanks, but they are the pawns of the army. In the right place, getting a simultaneous Guide-Doom-Misfortune cast with a unit of these guys will kill almost any other unit in the game. But you probably won't get that chance most of the time.
Use them to get position, to take some points, and to hold up more expensive enemy units. Keep them in cover and out of Assaults (Battle Focus is great here, popping in and out of cover, or running backwards as you shoot at an approaching assault unit.
Remember Bladestorm, that makes these dirt-cheap units a potential shutdown for those pesky Flying Monstrous Creatures (even more so, just Monstrous Creatures). If you can get them to the back field, they're excellent at overwhelming and taking down units like Broadsides and Riptides that are exposed. Zip them up in a Wave Serpent (and I hope you have a Farseer on the field) and drop them in a place to shoot like crazy, then Battle Focus back behind their transport for cover.
...But also remember that if you don't kill it, a Riptide with an Ion Accelerator can kill the whole squad in one shot.
Taking Guardian Defenders is akin to intentionally making the game harder. They have a lot of potential, but you'll need some luck, and you have to use them carefully. Definitely NOT a unit for beginners.
I hope that was informative!