help, best option for sound on the go?i-pod or new

what gives the best sound on the go?
i-pod,new digital walkman,mini disc,casette or portablecd
I use an iPod 3rd gen with a 40 gig drive, played through Etymotic ER-4P canalphones. I have my entire 500 CD collection stored in the iPod at 128kbps AAC.

I have read the sound will be beaten by a good CDP, but I can tell you the sound is extremely satisfying for me, and IMHO, the ease of use and storage of the iPod make it a no brainer decision. There is a reason it is crushing the competition.

I also highly recommend the ER-4P...totally blocks out outside noise, and the sound is remarkable. Only reason not to get is if you like accentuated or boomy bass (versus subtle yet accurate bass).