Windrider Jetbike squadrons are composed of Guardians on jetbikes armed with twin-linked shuriken catapults. Fortunately, the jetbike gives the model a 3+ armor save, making them just a durable as a Space Marine. This may not sound like much, but it’s tremendously durable for any Eldar not made out of wraithbone. In addition, Eldar jetbikes can move 36” with turbo-boost and can move 2D6” in the Assault phase, even if they don’t assault. Overall, this makes them one of the most mobile scoring units in the game, on par with Necrons in a Night Scythe.
Windrider Jetbikes are the most mobile and durable Eldar Troops, but they won’t be doing too much damage to the enemy. Each bike is armed with a twin-linked shuriken catapult, which isn’t bad but is very short ranged. One in three bikes can take a shuriken cannon, which gives them a bit more bite.
Windrider Jetbikes have one main role in the Eldar army: mobile scoring units. You can take units of three bikes for an absurdly cheap points cost, keep them out of danger for most of the game, and then jump on objectives in the final turns. These units won’t kill the enemy, but they will win you games.
Larger jetbike squads are useful for guarding a jetbike Farseer if you don’t want to pay the points for the rather expensive jetbike Warlock unit. For a relatively cheap price, they can absorb damage for your Farseer as he provides mobile psychic support. Again, they won’t do much damage to the enemy, but they’ll be a very important part of your army.
If you’re looking for a unit to hold objectives in the backfield, Rangers are your answer. They’ve got the statline of Guardians, but carry a sniper rifle and have the Infiltrate, Move through Cover, and Stealth special rules. With all these special rules, they’re still a point cheaper than Dire Avengers.
Like the Jetbikes, Rangers won’t be doing a whole lot of damage to the enemy (though they’re great for chipping wounds off monstrous creatures). However, they can hunker down on objectives in cover and happily survive the game. I don’t think a Ranger based army will really work, but a squad or two of Rangers to hold important objectives will be a good investment in most games. Even in kill point games, they can stay in cover and go to ground and be really difficult to kill.
Note: If your army includes Illic Nightspear, you can upgrade your Rangers to Pathfinders. These elite infiltrators are discussed in his entry.