what's the fastest way to level your pokemon up in pokemon x and y?
In XY I just fought the Elite four with Lucky Eggs + Exp O-Power, pretty slow but doable.
In ORAS is stupidly easy to level up, the Elite four has rematch with higher levels (around Lv70) and the Blissey trick is the best way to level up your Pokémon in the franchise.
If you have the patience to level up the Battle Maison, you can get a fuckton of exp from the Audino trainers. It's mostly useful for being able to level a level 1 Pokemon up to 40-something in one battle.