Disclaimer: I am leveling Astrologian, and thus do not have any experience with endgame content as AST, so I won't talk about that.

As a leveling AST, I feel like all of my cards (even Spear, what's so wrong with this one?!) have an impact in my level range. I throw a Balance on the highest level (or melee if both are equal) DPS, I throw Arrow on casters, Spear on Tank or Arcanist(Scholar) for their Aetherflow, Spire on tank (this regens a lot of their bar, holy crap), Bole on tank, and Ewer on either a non BLM caster or myself. I feel good with any card I Draw, and with Royal Road, that just makes things even better.