Bronze: Blind is a good choice for a melee or ranged weapon user, but useless for a pure caster Seraphim, who should take the more defensive Distract instead.
Silver: Either choice is good. T-Mutants appear in almost every region, yet they are still uncommon to find unless the player seeks them out. Undead, on the other hand, swarm across huge swaths of Tyr Lysia, The Swamp, and the Cursed Forest, not to mention many dungeons. Therefore, Purify might be a better choice unless the Seraphim is specifically going after T-Mutants on a regular basis (remember also that many bosses are T-Mutants).
Gold: Eagerness might be the better choice, as it will inflict more damage per second, killing enemies quicker. The range is already pretty good to begin with, it increases with CA level and can be further boosted by the combat art range item modifier.