(Fuck, now I've gotta look up stats...)
As he looked it up, he'd note the main advantages to each, such as the High Speed of Jolteon, the High HP of Vaporeon and Flareon's strong attacks... But the more he looked, the less those stats would matter, and the more the physical appearance would take over. Every Umbreon he saw seemed to have large breasts, but little else to them, whilst Leafeon's would match the chest and have a bigger ass. Of course, that wasn't to say that muscled Flareon girls were bad to look at, whilst Jolteon, Glaceon and Vaporeon all had similar, lithe physiques, Jolteon's that of a runner, Vaporeon's a swimmer and Glaceon somewhere between. As for Espeon and Sylveon, they had similarly petite frames, but just considering the ways Psychic could be used was hot enough, and Sylveon's ribbons...
(So, I'm basing chest sizes on Physical Defence, because why not. As for the rest... Eh, I have no logic.)