Wait for pricing details on the Moto Z. Then decide which is best for your usage pattern.
The OnePlus 3 has the advantage of a larger battery and a lower resolution, more power-sipping screen plus hardware, but the Moto Z has the advantage of a higher resolution display, some Moto tweaks and Motomods.
Oh, and the OnePlus 3 has a built in headphone jack. The Moto Z doesn't have one built-in, but a USB-C to 3.5mm adaptor is supplied.