I like them all, but eevee itself is still my favorite.
If they existed I would prolly like "Mithreon" (my metal type) and then "spookeon" (my ghost type).
Basically the real versions if they ever make them, those are the ones I invented though.
hell there should be an eeveelution for every type
bug=entomeon
dragon=drakeon
fighting=kampfeon (it'd be probably the only biped eeveelution)
flying=cieleon (it would be the first true pure flying type, i say "true" because of the type altering capabilities of kecleon's color change, porygon family's conversion attacks, and arceus holding a sky plate)
ghost=phantaseon
rock=petreon
ground=sableon
poison=otraveon
steel=acereon
normal=neutreon, eeveeon, hell even mega eevee would work (for the hell of it)
necroedit:
this was made before gen V which debut tornadus as a pure flying type