Selene skills

[Pells]

She will use it on *any* debuff, but she will only use it when a debuff is there.

If your tank is a warrior, she likes to blow it on the post-berserk pacification.

[Sailysium]

I find fairy swapping to be the most efficient thing to do when possible. For 4 man I generally use Eos on trash mobs since her buffed heals and mitigation allow me to contribute more AoE dps than if relying on selene's speed buff for the 30 sec the mobs are even alive for. But when fighting the bosses I'll swap to selene since the speed buff over a longer duration is more meaningful and damage to tank isn't as heavy as the large mob pulls.

8 mans I generally find parts in fights during progression where I can keep selene out but swap later on to eos when healing gets intensive (and vice versa).

My main issue with the fairies overall is that their utilities aren't really balanced with each other. All of Eos' abilities are very effective for healing raid damage but selene's tools are a lot more limited in application. With the silence being almost completely forgotten and the AoE leeches being handy but VERY situational, Selene's dps support tools don't weight as equally in my mind as Eos' healing support being offered. IMO i'd prefer if selene's silence were replaced with a different raid offensive utility to better balance against how much Eos has to offer.