Which would one you have out of these groups?
Eevee, Vaporeon, Jolteon, Flareon
Espeon, Umbreon
Leafeon, Glaceon, Sylveon
Choose one from each group!
My list:
Flareon
Can't decide between Espeon and Umbreon (maybe Umbreon)
Glaceon
If I had to pick just one from the first group, probably Jolteon, but then I like all three of the first Eeveelutions for different reasons.
Espeon, hands down. I like its shiny, besides.
I always wanted to give Glaceon a proper try, but other than one or two I tried raising, never really got far with it.
More Eeveelutions seem inevitable, and it make sense flavor-wise for Eevee, but I do wish Game Freak would give other old Pokemon split evos to choose from. Not as MANY per 'mon as Eevee, though. That'd be silly...?
Group A I'd choose Eevee only so I can breed and get more Eevee to evolve into the first Gen Eevelutions
Group B I pick Umbreon because I've always liked its design.
Group C I choose Sylveon because it is much easier to obtain than the other two and I can evolve Eevee into one literally anywhere that won't activate the evolving process to get Leafeon or Glaceon.
Eevee
Espeon
Sylveon
would give you the potential BIS for those groups and flexibility
Jolteon, Espeon, and Leafeon. Those are the best ones period.
I like Sylveon, because it looks so different from the other Eeveelutions.