SanDisk Extreme Pro is one of the best, in my opinion, they excel in IOPS for small random read and write which is especially important when using it in a computer like Steam Deck or Raspberry Pi. A lot of other SD cards are optimized for cameras where it is writing a lot of sequential data, but are slower in small reads and writes.

Because there are orthogonal performance properties and making them all get “better” with a higher “performance” number would be very expensive. Someone taking photos wants high capacity. Someone taking 8K video wants high write bandwidth. Someone playing games or as phone app offload storage wants high IOPS.

It’s why yo can buy a 1TB low-IOPS card for $40, or you can buy a 256GB high-IOPS card for $40. But if you want 1TB with high-iops, you’re going to pay about $200.

The Steam Deck is spec’ed with a UHS-1/SDHC slot, which means that you can’t use SDUC-class cards and you won’t get much benefit from using comparable cards with a UHS-II/UHS-III bus mark compared to one with a UHS-I mark, even if the other marks otherwise suggest better performance. You can basically ignore the A/V markings because they’re not granular enough to help with comparing cards at this particular performance level (you should instead compare “Random Read”/“Random Write” performance benchmark scores).

Note that there remains a considerable amount of variance among similarly marked cards. For example, the Sandisk Extreme Pro (Bus: UHS-I, Speed: 3) can benchmark write speeds which are almost twice as fast as the Sandisk Extreme (Bus: UHS-I, Speed: 3).

tl;dr: The ideal card will have the following markings:

• Capacity Standard: SDXC (SDUC is not compatible)
• UHS Bus Speed: I (higher is fine, but not helpful)
• Speed Class: 3 (though you should really be comparing benchmark scores instead!)