Flareon! This comes from someone who has used a variety of Eeveelutions as complementary (and main) team members over the years and generally isn't too big on Eeveelutions. I already liked it before using it because it's the closest thing we have to a bigger, fluffier, chonkier Eevee, but when my Sizzly became a main team member in LGPE, he gave me all the more reason to like it. I wish he had more viable movepool options, but he's perfect as he is. I love my fluffy boy.
Call me a Genwunner here, but the other two original Eeveelutions don't trail too far behind. I find both Vaporeon and especially Jolteon (third and second favourites respectively) to be more adorable than any of the later Eeveelutions. They give me less of a... "plastic" vibe and look a lot more huggable. Neither of them have disappointed in the battling aspect either; I haven't used Jolteon extensively yet, but I have the feeling it'd be very useful in a mono-Electric run!
On an additional note, I have also found myself more fond of some well-known fanmade Eeveelutions, such as Scaleon from Xenoverse and Nucleon from Uranium, than the post-Gen I canon ones. Scaleon gives off the "classic" vibe I look for in Eeveelutions, whereas Nucleon turns the "plasticity" that I dislike in later Eeveelutions into a strength - because it's supposed to be artificial! Take it with a grain of salt, but I do hope Game Freak' designers take a long, hard look at what makes the OG Eeveelutions so charming before designing new ones.
