Alphanumeric is the most efficient QR code encoding mode.
(Just to further make this clear, for QR Byte encoding uses ISO/IEC 8859-1, where 65 characters are undefined, so 191/256, which is ~75%. If character encoding isn't an issue, than byte encoding is the most efficient, 256/256, 100%, but that's a very rare edge case. Also, last time I did the math on Kanji it was about 81% efficient. *I have not dug too deep into Kanji and there may be a way to make it more efficient than I'm aware of. I've never considered it useful for my applications so I have not looked.)
Not according to my math:
Numeric: 1000/1024 = 98%
Alphanum: 2025/2048 = 99%
Byte: 191/256 = 75%
Kanji: 13/16 = 81%*
Alphanumeric is the most efficient QR code encoding mode.
(Just to further make this clear, for QR Byte encoding uses ISO/IEC 8859-1, where 65 characters are undefined, so 191/256, which is ~75%. If character encoding isn't an issue, than byte encoding is the most efficient, 256/256, 100%, but that's a very rare edge case. Also, last time I did the math on Kanji it was about 81% efficient. *I have not dug too deep into Kanji and there may be a way to make it more efficient than I'm aware of. I've never considered it useful for my applications so I have not looked.)