The 1997 vintage being the most sought-after, in general
You can only use this effect of "Materiactor Gigadra" once per turn
Beat him in a duel and he'll ask you to point out some easy prey for him, do that and he'll do the same for you
You can only use this effect of "Auram the World Chalice Blademaster" once per turn
The question is whether it's better to use Solemnity in this role over Anafenza, Kin-Tree Spirit or Melira, Sylvok Outcast, and while the answer is generally no (mostly because Anafenza and Melira can be found with Chord of Calling and Collected Company while Solemnity cannot), it's worth keeping in mind because, as an enchantment, Solemnity is much harder to kill than a random Grizzly Bear
Szarekh, the Silent King The problem with Szarekh, the Silent King is that needing to attack is a really slow trigger condition and one that you can only do once per turn