Most cards today are either UHS-I or UHS-II. That doesn't refer to speed directly, but it's closely related. It refers to the type of interface between the SD card and the camera. A UHS-II is potentially faster, but only if both the card and the interface are compatible with UHS-II technology. The Canon M50 has a UHS-I SD card slot, so ideally you'd use a UHS-I card. However, the system is designed to be backwards compatible. What that means in practice is that you can use a UHS-II card in the M50, but it will be treated as though it's a UHS-I card and you won't get any extra write speed benefit.