Not sure if this topic should be here, but here I go;
1. Fuegan & Spiritseer + Warlock Council
Why? => Fuegan purposely fails & absorbs max 2 wounds (plasma/melta/lascannon shots..etc). Then, Spiritseer or any of the Warlock Council members that managed to get the Destructor/Renewer spell will cast it to Fuegan. Theoretically can keep repeating this until he gets to S10 A10.
Fuegan can also do the run & gun double-tap tactic as per the Avatar below, but even better with Firepike's range of 18".
2. Avatar of Khaine & Farseer/Eldrad
Why? => Can move 6" + run d6" (can re-roll with Fleet) & then shoot meltagun TWICE with Fast Shot. In challenge, use Disarming Strike to turn 1 enemy cc weapon (power weapon, force weapon, daemon weapon, any weapon) into a normal cc weapon.
Farseer/Eldrad to buff him with Fortune.
So, what's your favourite Eldar HQs?