This is for free players and for members who do not wish to spend $99.95 for 40k AC's and an IDoA:

As soon as possible, kill Diabolical Warlord for Burning Blade.

At level 80, do the Celestial Arena for Burning Blade of Abezeth.

This is for all players:

At level 85 - 90, start grinding the Necrotic Sword of Doom.

Obtain at least the following classes:  Legion Revenant, Stonecrusher, ArchPaladin, and Lord of Order.  Preferably Void Highlord as well.

Obtain the Head of the Legion Beast and / or the Ascended Omni Cowl.

Do Ultra Boss fights for their items. although make sure you come prepared!