That is a very different question.
I love water-types so Vapoureon is a natural choice-
But Jolteon is so hardcore, and I really like that he learns pin missile-
But neither of them are cuddly, so Flareon is an especially good choice for a starter because the only gen that I liked the fire starter was cyndaquil (and there are not many fire type pokemans!)
Mmm... I never really found a good skill set for Umbreon/Espeon and I'm training an Evee in silver right now, giving him daily haircuts, proteins etc, and everything I can do to make him happy and leveling him up slowly (Evee is 30, rest are 35) and it still hasn't evolved - so in short I never found these guys worth in, but I do like them in theory.
Leafeon/Glaceon (I haven't played much D/P unfortunately) but once platinum comes out I'm going to get that and play through the game (I've played through once but going as fast as possible - which means I didn't get to beat the elite 4 cause my party was weak) But when I do play again, I will definitely train a Glaceon