I remember ATRAC was always being slated but I thought the quality wasn't bad. Trouble is I don't know how one could do a sensible comparison as I don't believe there are any ATRAC encoders available for PC (correct me if I am wrong). Certainly, AAC at 320Kbit/s is going to be pretty good.
A lot depends on the Encoder and encoding options as well. Also, if
you spend enough time experimenting, you will find for some tracks 128
kbps is as good as 320 kbps. Depends on a lot of factors.
advice is: select one format and stick to it. Choose VBR with High
quality if your encoder has them and choose 256 kbps as lower boundary
and highest available as upper boundary. The best one time setting.