There are two contenders that I use right now. One made by Delkin and the other made by Sony. This Delkin card is rated to sustained the same bandwidth as the Sony. In practice there is basically no discerning difference while shooting on the Nikon Z6/Z7 and D5/D4.
While I kinda like the idea of Delking promising a replacement within 48hrs. I have not need to replace any of my XQD cards and that is because the technology used is made to sustain lots of read and write at all speeds while being able to contain its data integrity in a way making it fail proof.
Delkin XQD memory cards specifications:
- XQD Format Version 2.0 Compliant
- 2933X Speed Rating
- Max Read Speed: 440MB/s
- Max Write Speed: 400MB/s
- Records 4K & Full HD 1080p Video at High Frame Rates
- RAW Continuous Burst Ready
- Supports EB Streaming
- Serialized Like Your Camera
- 48HR Replacement Guarantee
In its current phase, the Delkin card is a little bit pricier than the Sony, but I’m sure soon that will change. These cards are serialized to combat fakes out there. These cards are available now: Sony and Delkin
There seems no other alternatives exist at the moment.