I usually use my Samsung S3 for my daily commute paired with my Denon ah -c400 and the sound wasn't bed. I have a cowon too, but can't use it with iphone compatible jacks such as the new range of denons (the D600 comes with a normal cable so that's great).
I just bought a sansa clip zip because it was so cheap and the difference between that and the S3 is night and day. I can honestly say the S3 really has poor for audio.
The sound from my iems using the sansa is very very good and benefits immensely from the sansa's amp (I've only tried the Koss Porta Pros and ah-c400's so far), twice as good in fact as the S3.
The base on the ah-c400s is actually rather good, first time i tried them I thought, oh no I made a mistake, but after a month or two the base is actually prtetty decent.
I personally think the ah-c400s are possibly the best bargain on the planet at the moment, for all genres of music, they really are beautifully balanced.
There was a lot of talk about base distortion at high volumes when they first came out. I did notice this myself, but now a few months down the line the mild distortion is gone, must have just been a settling in period. That's the thing most reviewers have the phones for a week or two, which for some phones is not enough time.
Anyway if you use a Samsung S3 for audio, you are doing your ears no favours, go buy a clip for 20 bucks.