Our guardian has killed gods and thousands of enemies at this point, why don't we have a nemesis or a group coming after us? Think about how cool it would be to have a dlc, where the enemy was focused on destroying our character. Not the city or the universe, just destroying our character's life. I feel like that would add some depth to our guardian's story. Anyway, I would choose Fikrul, Kelgorath, Kinox, Taniks, Nezerec, and Eramis.
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If we're limiting it to characters that are currently alive (or otherwise capable of returning), I think your list is pretty spot on. If we're picking a best of from the Guardian's past, I'd say Oryx, Eramis, Ghaul, Taniks, Aksis and Fikrul. I don't see any vex minds allying with any of the others on the list but if we had to have a vex included I would replace Aksis with the Undying Mind.