Good question. I guess Leafeon and Vaporeon.

If only one I’d choose Umbreon.

Reason because it’s cool looking and etc.

Ps stay on topic..

UMBREON

I love it so much you don't understand

Dark is my favorite type, and Umbreon has a cool design. Plus, it has a really good shiny, better than all the other eeveelution's shinies, imo.

I could rant about how awesome Umbreon is but I'm not gonna