Thom Hogan

If you own a Zf, Zfc, Z30, Z50, Z50II, or Z5, the situation is simple, and what you need to do is clear:

• Z30, Z50, or Zfc owner — Buy UHS-I capable SD cards of at least 95MBps speed. Make sure they say U3 for video capability.
• Z50II, Z5, or Zf owner — Buy UHS-II capable SD cards of at least 300MBps speed. Make sure they say U3 for video capability.

Anything less than what I reference above may cause you issues, though for basic still photography that isn't continuous, pretty much any old SD card should work. 

• Z6II, Z6III, or Z7II owner — Buy CFe (CFexpress) Type B cards of any speed for the first slot, and UHS-II capable SD cards of at least 300Mbps that are also marked U3 for video capability for the second slot.
• Z8 owner — Buy CFe (CFexpress) Type B cards with a high-sustained write capability (not what's printed on the outside of the card!) for the primary slot. These include Angelbird XT, Delkin Black, Nextorage B1 Pro, and ProGrade Cobalt cards. This is important if you want best possible buffer performance and/or record 8K raw video. The difference in maximum sustained write capability is as much as 140MBs in a cheap card versus 1480MBs in a high-sustained rate card! Buy UHS-II capable SD cards of at least 300MBps speed for the secondary slot. Make sure they say U3 for video capability.
• Z9 owner — Buy CFe (CFexpress) Type B cards with a high-sustained write capability (not what's printed on the outside of the card!). These include Angelbird XT, Delkin Black, Nextorage B1 Pro, and ProGrade Cobalt cards. This is important if you want best possible buffer performance and/or record 8K video. The difference in maximum sustained write capability is as much as 140MBs versus 1480MBs! 

It's the original Z6 and Z7 owner—the initial models only—that frets the most over cards. That's because of the XQD slot in the camera, which has been upgraded to support CFexpress (Type B) via firmware updates. 

XQD has a bit of a history. Originally, XQD was going to be the future of CompactFlash (it still is, only it evolved to CFexpress). But SanDisk dropped out of the development consortium with Nikon and Sony nearly at the last minute before launch, and instead launched CFast, which Canon endorsed and adopted. 

The original launch of XQD appeared in 2012 with the Nikon D4 (DSLR) camera. Early XQD 1.0 support came solely from Sony and Lexar (then a part of Micron). The earliest XQD cards had speeds of 125 to 500MBps, and used a simple one lane PCIe 2.0 bus interface. XQD 2.0 introduced a newer two lane PCIe stack and 1GBps speeds. CFexpress (Type B) is physically the same as XQD, but uses PCIe 3.0 with two lanes in version 1.0, and now four lanes in version 2.0. 

Here's the problem with XQD and CFexpress: while it seems it should be just mix-and-match, it isn't. Early XQD cards may not work with current card readers, CFexpress cards don't work with (most) XQD card readers, your Z6 or Z7 has to be updated to new firmware to use CFexpress at all, and a host of other subtle issues all seem to crop up. 

Here's a simple solution for original Z6 and Z7 users: buy Sony G series XQD cards and a card reader for them (Sony makes a couple). A Sony 32GB XQD G series card costs US$90 as I write this, 64GB is US$130. Nikon seems to use Sony cards for validation these days, and I've never had any issues with the current G series cards in my Z's. Indeed, the hard to find Nikon-branded XQD card appears to be a Sony underneath. I have had an older, no-longer-made, Lexar card hiccup in the Z bodies. And I've had both older Lexar and Sony XQD cards have issues with current XQD card readers. So make sure you buy current XQD. 

Wait, why not buy a CFexpress Type B card? Well, you can. You'll need a CFexpress Type B card reader, too, as the XQD readers generally don't work with CFexpress because their drivers were never updated. But CFexpress doesn't net you any additional speed in the Z6 and Z7 bodies. In fact, once the buffer fills, a CFexpress card won't shoot as fast as a (supposedly slower) XQD card! Moreover, not all CFexpress cards are cleared for use with the Z6 and Z7. As with XQD when it first came out, there seems to be some difference of opinion on how to interpret part of the specification. SanDisk's first CFexpress cards, for instance, didn't work properly in the Z6 and Z7 and had to be exchanged.

Note that SanDisk is back. I wrote earlier that XQD/CFexpress is the future of CompactFlash. That's now clear given that all the members of the CompactFlash organization are supporting CFexpress. But in terms of the original Z6 and Z7, these are XQD cameras that can be made to work with CFexpress. So the proper card for them, in my opinion, is a Version 2 XQD card, and the best and most consistent of those I've found to date is the current Sony G (there were two previous generations of G, which just confuses things even more). 

All that said, if you shoot really high volumes of shots at a time (e.g. sports, wildlife, or events), you may want to use a CFexpress card in your Z6 or Z7 for one reason: your XQD card and card reader is going to top out at 440MBps transfer to your computer, while your CFexpress card and card reader is probably going to hit somewhere above 1500MBps, at least if you have the right ports on your computer to support that speed.