Unless fiesta gold players really know if the Monster is Strictly Defense.
When it comes to Monsters and Bosses, there are some Monsters or Bosses that just have Defense and that is it. Damage Rings would be ok if you wanted, but we have personally tested and the Poison Damage Gems do more Damage Rings.A few Monsters we tested this on was in Avalon, it was the Pirates and those Red Apes in the elevated/middle part of the Island. We were in the 100-110 Stage Farming Earls, and this is when we noticed the difference in Damages, as at these Levels we didn't really need those Def Necklaces as much.Unless fiesta gold players really know if the Monster is Strictly Defense and not any Poison Resistance, we would recommend using Damage Rings just because it ensures you get more Damage if you need it, but if you know a Monster/Boss is all Defense and you think you do not need the Defense Necklaces we would use the Poison Damage Rings.