I like them...although Jolteon and Leafeon's designs don't particularly stand out, I love using Jolteon.
Flareon, I just wish would get a cool egg move, something powerful and physical, or maybe Extremespeed like Arcanine, as Flareon is awesome.
Vaporeon, is, well, used in OU battling, even I can use it, it's so good.
Glaceon is awesome, because of it's Special Attack
Espeon is awesome because of it's evolution method, it's typing, and it's speed and special attack.
Personally, I've used them all at different times on different games:
LeafGreen: Flareon,Jolteon,Vaporeon
Diamond: Umbreon,Leafeon
Platinum: Flareon, Umbreon, Glaceon
SoulSilver: Espeon (currently so awesome, it beat Chuck with Shadow Ball)