Latias is my all time favorite
Lugia is a close behind Latias, as Lugia is just...BEASTLY!
Mew is the cutest Pokemon of them all!
Espeon is my favorite Psychic normal Pokemon & Eeveeolution and I always use HER, yes I train female Espeons
Gardevoir would be 2nd, most used in the 3rd Generation by me.
Latios, because of his twin sister, is on the list as well :) (Can't like one and not the other, ya know?)