The absolute best place in the game for egg hatching in X and Y is definitely Centrico Plaza in Lumiose City. Because of the plazas circular shape and the angle from which you view it, if you walk to the right, you will walk around the circle continuously without stopping, provided you don't move in a different direction and there aren't any NPCs in your path. Due to this, if you position yourself so no NPCs are in your path and stick a quarter (or a coin of similar size) underneath your Circle Pad so that it's stuck moving to the left or right, you will continuously move left or right (This video shows the whole process pretty well). From there, you can walk away and do something else while your steps add up, and come back about 10 minutes later to find your egg hatched and ready to go!
Hope I could help!
