[Psycho]

If you are comparing vine and gold shields, I'd say that gold shield has a better overall value.

You would prefer vine shield for troops with MR lower than moral - undead, ulmish troops, animals (monkeys). On the plus side compared with gold shield, it disables the target for at least two rounds as opposed to one. A niche combo can be achieved with evening star which reduces target strength on hit (no MR check), thus making it harder to release from vines.

Gold shield is better for troops where moral is lower than MR - that is usually more elite troops and thugs. Most thugs (Van, Eriu and the like) have 17-18 MR, but 14-15 moral. In addition it has much better parry and protection values, so it's overall more useful. Plus it needs 1 gem less to forge and needs less valuable gems (fire and earth compared to nature). There is the synergy with fear as well.