Selecting a microSD card

Lego recommends cards with Application PerformanceClass A1 Application Performance Class. The size should be between 4 to 32 GB (more is not supported).

The old microSDHC speed classes 2/4/6/10, UHS-I/II/III, U1/3, 500/633/1000x don't really matter because they only care for sequential read/write of single large files, like they're needed for storing picture or videos. An EV3 (or Raspi, ...) needs to work with lots of small files with random access. That's only incorporated in Application PerformanceClass.

It looks like this article has some helpful information: http://www.theatreofnoise.com/2013/08/choosing-micro-sd-card-for-your-phone.html

Benchmarks:

• https://www.jeffgeerling.com/blog/2018/raspberry-pi-microsd-card-performance-comparison-2018
• https://lechnology.com/2017/04/microsd-card-benchmark-for-ev3-and-raspberry-pi-3/
• http://www.pidramble.com/wiki/benchmarks/microsd-cards
• http://jgp.net/microsd-card-performance-raspberry-pi/