I've heard good things about the audio quality of Cowon players. Sorry, can't speak from personal experience. Do you ever see these players in stores in your country? In the US it's often difficult to find any of the lesser-known brands in brick and mortar stores. Archos had a deal with Sharper Image for their '04 series, but I don't think they carry the new line.

It's funny, though, I was just looking at the Cowon Q5W this morning. That player looks fantastic, and I've been waiting a long time for a player in this form factor to have a full-face screen. This one seems to have everything I look for in an MP3 player, plus it'll play SNES games, apparently - a feature that appeals to me greatly (it always was my favorite video game system).

*edit*
There are reviews up for both the players you're looking at here. I've never liked the design of the Vibez player, but I hear the audio quality is good.