Which audio quality is best 128k or 256k?

Audio file bit rates are measured in thousands of bits per second, or kbps. I mentioned above that a CD contains audio at 1,411 kbps, and when you convert that audio to a lossy file, its bit rate is much lower. A higher bit rate is better, so a 256 kbps MP3 or AAC file is better than a 128 kbps file.