In terms of appearance, it's gotta be Espeon for me. Personally, I find it way too adorable. It's not so bad when it comes to battling, either. It's got access to both Light Screen and Reflect, and is fast enough to set them up successfully. Just give it some Light Clay, and it's all set! It's got Magic Bounce ability, too, which makes it even more useful; it throws back all non-damaging moves back to the opponent, such as Stealth Rock, Spore, and Confuse Ray. Other than that, I like Vaporeon as well. :)