EDIT: I've revisited the Autarch, as well as making a minor adjustment to his equipment. See more about that here.
According to the fluff, these individuals represent the ideal Eldar. The pinnacle of what an Eldar can hope to be/achieve. I find this ultimately sad, given that he's nothing like the rest of the Eldar. The vast majority is deemed "not good enough."
Autarchs are said to have walked every path, and when he felt he mastered it, mustered the strength to turn from that path and take another. While most Eldar are currently walking one path or another, a good amount remain "lost" on these paths; becoming obsessed with a path to the point that it becomes an addiction is a very real danger to them. These lost addicts are better referred to as "Exarchs." Or, in the case of one specific path, "Farseers." While the Eldar society does find these individuals extremely useful (in that they gain in power along their path more than a normal Eldar would, and remain to teach Eldar currently traveling that path) they pity them. For the Eldar, life itself is a constant trial. They strive endlessly to keep themselves from descending back into the very depravity that brought about the birth of She Who Thirsts, and simultaneously heralded the decline of their species. Exarchs are a step away from Dark Eldar in the minds of the normal Eldar populace.
Autarchs are their antithesis. Where an Exarch is specialized to the extreme, having a kind of tunnel-vision view of life, an Autarch has had the wisdom to learn from all paths and take this learning with him through life. He combines his knowledge to make him a stronger individual as a whole. Because of this, the Eldar populace views him with awe, and gives a lot of weight to his words. Naturally, Autarchs take up leadership roles in their craftworlds, so that they can benefit from his more holistic view on life.
Having travelled every path, only an Autarch understands the role each Aspect plays on the battlefield, and this is represented in his special rule. Rolls for reserves benefit from a +1 while he's on the battlefield, allowing you to perform much craftier maneuvres with relative stability.
Following this description of what an Autarch is, I decided to equip mine with the equipment to enable him to join and help nearly any Aspect I field. I say nearly, because all is impossible. So I decided to weed out a few that would hinder his ability to assist the rest.
If I equipped him with a Reaper Launcher, his role would be shifted backwards, away from enemy lines. This would hinder his ability to bolster a front line by distance alone, so that was out. I decided, rather, to focus on the mid to close range Aspects so he could easily move between them.
Close Combat: Mandiblasters and a Power Weapon. The other option was a Scorpion Chainsword and Banshee mask. While highly tempting, I disregarded the Chainsword (and its +1 S) because it would specialize him more between Scorpions and Banshees. Scorpions are about high number of attacks against low armoured foes(the high S helps, but it's really about # of attacks) and the Banshees are about killing mid to heavy armoured foes. By giving him the chainsword/mask, he'd be a hell of a help to the Scorpions, but not so much to the Banshees ... the lack of an Armour-ignoring weapon decreases his effectiveness in their role. If I give him the Mandiblasters and a Power Weapon, now he has the high attacks to fit in with Scorpions, AND the ability to ignore armour like the Banshees. This was my reasoning behind this choice.
Mobility: Jetbike, Swooping Hawk Jetpack, Warp Spider Generator.
To be honest, the only reason to take a Swooping Hawk pack over the other two is if you intend on having him join the Hawks and benefit from 'Skyleap.' The Warp Generator does the same thing, with the addition of allowing him an additional move during assault if he's not assaulting. I guess people just like the flashiness of the wings, because I see this taken more than any other choice. I chose the Generator because it was simple and effective, while also giving me more options that the other two don't allow. Taking the Jetbike will hinder my ability to join other squads, adding my strength to theirs ... unless you have jetbike squads.
Gun: Shuriken Pistol, Reaper Launcher, Fusion Blaster
Ok, I'm gonna stop right there. I know there are more, but Fusion Blaster is all you need to hear. Adding the mobility from your previous choice, you would now be able to quickly take down that pesky tank that your Dragons would take another turn (maybe) getting to. Being that it's an assault weapon, it's also a nearly guaranteed kill before a charge. It's just too awesome to say 'no' to.
