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.
I think that Minidisc do have a bricks and mortar store, but over the other side of the country from me unfortunately. I have never seen Cowon players in any major electronics retail chain stores here, so no chance of listening before purchase, but most reviews appear to rate the sound quality well with MP3s; I would be using FLAC, or ogg at Q10 so the source material shouldn't be a limitation.
I've never liked the design of the Vibez player, but I hear the audio quality is good.
Hardware design (and even software interface) is not a big issue for me, as I usually just shuffle through all tracks so I rarely touch the controls after power-on, but good audio quality is a must, hence the questions. I have heard good reports about the Vibez' audio quality, but it is so hard to get a Vibez here that I have misgivings about after sales service (maybe I am mistaken).
The Q5W does look like a nice player (expensive here though - $850 for 60GB!). The main worry I would have with that one is the large, relatively fragile screen, not exactly pocketable without a case, and probably too big with one anyway!