i own around 4 of them before.  d303 has the best phone out.  I love its detailed and warmed sound signature.  I found the sound quality beat all the recently mp3 players as of 5/11/201.  It also has very good line out but d555's line out is better than d303.  the optical out is a plus if you use it to sync with your mini disc.   d303 has most common issue with the RF-410CH spindle motor and you often see skipping problem with that.  in most case, if you hold the discman vertically it will play without skipping.

People call this King of the Sony Discman.  Ebay used to have super high price on this item.   I own one before and the line out is super.  Phone out is not that powerful but very good for female vocal.