Argueable. Yveltal is my absolute favourite and Kalos has an amazing Pokedex so Y is a great choice. But Alpha Sapphire is an amazing remake. I loved Emerald, I love AS. But the most clean and modern game is Ultra moon by far. Choose according to this

I l▲ve U↑tra Sun an U↑tra M▲▲n because of N!h!lego. But X&Y are great games t▲▲ !