Quick question: Just unlocked SCH and I'm wondering when I should use Selene and when I should use Eos. Just looking at them it seems like Eos is generally the better choice, but I'm sure Selene is better in spots.
Basically, bring Eos if you think you're going to be doing more healing, otherwise bring Selene. Eos gives you 3 extra healing cooldowns- a party-wide HP regen, a party-wide 20% magic defense up buff, and a 10% buff to your own healing. If you don't think you're going to need these cooldowns, bring Selene- her Fey Wind buff speeds everyone up and adds a few percentage points to DPS, which means things might die a little quicker. For me, I only find that Eos's cooldowns are necessary in the highest level content, for pretty much everything else I bring Selene. But, if you want to have the safety blanket of having those extra cooldowns available, bringing Eos is fine. No one else is going care one way or the other generally.