The Witness isn't exclusive. It's a timed exclusive that will eventually come to PC and Xbox One.
What we don't know about the Xbox One exclusives is that are all these being released by Microsoft, or has Microsoft paid third parties to develop exclusive games for them like last gen. Microsoft only said that they're getting 15 exclusives within the year on Xbox One, and they'll probably get more, but that 15 doesn't necessarily mean they're from Microsoft.
That being said, I'd rather wait until E3, and while Sony might not put as many exclusives out, I think they'll get more exclusives overall the the Xbox One does.







