>>36558363The priority order is this: first Glaceon/Leafeon, then Sylveon, then Espeon/Umbreon.
So a max friendship and affection Eevee knowing a Fairy-type move leveled up near an Icy/Moss Rock will always become Glaceon/Leafeon
An Eevee with max friendship and affection and knowing at least one Fairy-type move will always become Sylveon
This actually makes sense when you consider that Glaceon, Leafeon and Sylveon need specific conditions to be obtained and you can prevent getting them by just not meeting that criteria (not going to an Icy/Moss Rock, or getting rid of Fairy-type moves Eevee knows) but once Eevee has high friendship, lowering that friendship to prevent evolution into Espeon or Umbreon will take much longer