You can't go wrong with these Micro SD cards.new-nintendo-3ds-01

The New Nintendo 3DS XL uses Micro SDHC cards, which is installed on the back plate of that handheld. You'll need a size number 00 Philip's head screwdriver to remove that back plate. Listed below are the Micro SDHC cards that's confirmed to be compatible with that handheld:

SanDisk Extreme microSDHC:

SanDisk Extreme PLUS microSDHC:

SanDisk Extreme PRO microSDHC:

Toshiba microSDHC:

Image credit: Nintendo