So, the SD Association is absolutely fucking insane when it comes to giving labels to literally anything.

The Steam Deck supports UHS-1 microSD cards.
That’s the name of the bus. There’salso UHS-2 and UHS-3, but they’re backwards compatible with UHS-1, so that’s whatever.

Speeds…
Some cards used speed “classes”, like Class 10…
There’s also U1 or U3 speeds (which is a speed rating independent of the bus. (A U3 cards is probably a UHS-1 card.
Some have a speed rated with a V, like V10, V30, etc.
They often have multiple labels too.
These can all be used to label the speed of a UHS-1 card:
UHS Speed Class

• U1: 10 MB/s minimum write speed.
• U3: 30 MB/s minimum write speed.

Video Speed Class

• V6: 6 MB/s minimum write speed.
• V10: 10 MB/s minimum write speed.
• V30: 30 MB/s minimum write speed.
• V60: 60 MB/s minimum write speed.
• V90: 90 MB/s minimum write speed.

Class 10

• Class 10: 10 MB/s minimum write speed (legacy).

Anyway, U3 is basically the same as a V30.
U3/V30 would be the minimum I’d get for the Deck. Price being the deciding factor for the rest.
I don’t really care if the card ever fails, so brand was irrelevant in my choice.