These two! Now THESE are the Eeveelutions I'm most familiar with. They remain my favorites of the bunch introduced to this day.
My absolute favorite of all Eeveelutions is Espeon. So it edges out over Umbreon. I always used it in playthroughs during Gen II and recreated it in my HeartGold. Its design is so graceful. A light purple feline with a gem on its forehead. It makes me think of Carbuncle from Final Fantasy. What a beautiful creature.
Although in recent years, I've come to like Umbreon too. I've used it a few times in Showdown and it has been really damn useful. Its defensive capabilities comfort me, as I prefer taking hits to exploding into death quickly. Also, it looks like my black cat and is also as simple and graceful as Espeon for the most part. I'm using it in my playthrough of Y right now, naned after my cat.
These two though, I just adore them. They're going to be the only Eeveelutions I own plushies of, as I have ordered them online.