I went with Data Matrix to backup my (encrypted) PGP key pair to paper. When I compared QR and Data Matrix, Data Matrix "won" because of its ability to encode

I went with Data Matrix to backup my (encrypted) PGP key pair to paper. When I compared QR and Data Matrix, Data Matrix "won" because of its ability to encode pretty massive amounts of data by chaining individual barcodes together. (QR tops out at around 3000 bytes; less if you increase the error correction level.) That said, I'm not sure if I'd make the same decision today. QR code readers are plentiful, and Data Matrix readers are comparatively rare.