The iPhone, because it gave way to the app store, freeing us from all the previous crappy phone experiences. Think about how many industries and new products were created from that product. Amazing.
I enjoy most Apple products, but AirPods were the first product I truly felt were magical. (I also think being a game changer doesn't necessarily correlate with being the best designed product of all-time... just a product that was better than the competition at its inception.)