Why don't we just stop bickering about everyone's bad math and say what kind of content you'd use which fairy in:

Coil 1-5: Selene unless solo-healing, or if the party is derpy and/or undergeared.
Primals HM: ditto
All roulettes: again, ditto
Primals EX: Eos, maybe Selene with good party
Coil 6+: ditto

See the pattern? If you're overgeared and/or echo buffed for the event, Selene, if not Eos.