At the top of the corporate world, Apple and Google are in a back-and-forth battle to be number one.It's not clear which of the two Silicon Valley giants will emerge on top in a contest which highlights the contrast of very different business models.For a brief time early this year, Google parent Alphabet overtook Apple as the world's largest company by market value.Apple then regained, lost and recovered the leader position in May in a battle that appears set to continue for some time.
