Umbreon, probably. As far as the eeveeloutions are concerned, stats don't play a big part, since there are fire pokemon far more powerful than flareon, and water pokemon far more powerful than vaporeon and all that, and for that reason I go by looks more than anything. Therefore, my favorite would have to be Umbreon, 'cause its black with gold/yellow rings that glow in darkness, I mean, seriously, its not not cool. And the Shiny one looks wicked awesome.