AAC 256kbps vs AAC 320kbps: Sound Quality. Which is better?

Most people are happy with AAC/256, but feel free to rip a few different ways and judge for your own circumstances. By the way it is not just your ears, but also your equipment and listening conditions. E.g., do you listen on high quality speakers in a nice quiet room, or using cheap earbuds while you ride the cross-town bus?

Also, note that the phrase "CD quality" refers to encoding that maintains the full 44.1kHz sample rate and 16-bit encoding as a CD has. But the actual audio quality on a CD can vary widely, especially with older vintage CDs.

Your own ears are the best judge. I doubt anyone honestly can tell the difference between the two you mentioned.

Originally iTunes was selling tracks at 120 and now they have upped that.

If I'm converting from a CD I own and it's one I use a lot, I use ALAC lossless. If I'm converting MP3 to AAC, I tend to use 192 as I originally used that when Apple were originally offering 120 so thought i would go a little above and I have continued to use it ever since. I tried higher ones and couldn't tell the difference. It was also dependent on the original source - if I was converting a 320 MP3, no point converting it to lossless as you are just filling the file with 1s and 0s and no relevant data.

In the end, your own ears decide.