I didn't actually plan to level certain Pokemon to level 100. It just happened when I heard that levels didn't automatically get raised when on wi-fi anymore.
First was my Volcarona (Modest, 31 IV Sp. atk), then my Flygon (Jolly, 31 IV Atk, Speed), then my Mienshao (Hasty, 31 IV Atk, Sp. atk, Speed), and finally my Jellicient (31 IV HP, Defense, Sp. Def). All of them from Egg to 100 and EV trained in literally a couple of days. My Jigglypuff from HeartGold was somewhere in between there.
Audino, Lucky Egg, Double Exp. Pass Power, Stadiums, Morimoto, Cheren, Royal Unova, and Elite Four make the daily grind so easy.