Ok, let's get serious.
I will define power.
Good moveset to match stats.
Rounded stats and covered weak stats.
Stats to fit moves.
Good competitive.
Good ability (minor point)

I am Masuda breeding for a Shiny Eevee. I loved that line for a long time, NOT JUST BECAUSE OF MY NAME!!!
Their design is original and the evolution thing is epic!
If there is a dragon-type Eevee called Draconeon, it'll either be Lucius or Malfoy. LOLOLOL
Well, I was talking about Eevees. I could evolve into any of these. DO YOUR RESEARCH before this. Find out about their Shiny design. And give me a good name for it. AW YEZUMS.
So, if my breeding works, my first shiny will come along. But, with Eevees, it's tough to pick.
Like CHARMANDERSQUIRTLEBULBASAUR.-.M'00

This should probably be in the Pokémon topic, but if you want the best shiny eeveelution then look no further than Umbreon.