In my experience, YesAsia is slow and CDJapan is fast. I once received a CD a day before its actual release date! And that was through REGULAR air mail, not even registered or EMS.
For YesAsia however, I sometimes waited weeks for my items.
That's why I only use YesAsia for stuff you can't get at CDJapan, which is basically:
- overseas versions. CDJapan only has Japanese versions while YesAsia also usually stocks overseas versions like Taiwan or Hongkong press.
- tour goodies. YesAsia has all of Ayu's latest tour goodies like AT08, PCDL08-09 and AT09. CDJapan never has goodies.
Hope I helped you