Rarity's contest team:

Magnizone(Cool):
It's electric attack are a work of art.

Milotic(Beauty):
Because you need to maximize beauty to evolve it, and it's the only pokemon that anyone brought up when I asked for help with this list!

Chimeco(Smart):
Because it's good looking and elegant. And the chime sound it makes helps her relax when making dresses.

Togekiss(Cute):
A cute, gentle pokemon. And good for looking after Sweetie Belle.

Smergle(Tough):
This pokemon's artistic mind is good for designing dresses. And he's good at any contest because it can learn ANY move set she want's it to.

Persian:
Because of Opalescence.