Hi fmo, nice to see you gave a variety of players a try before settling on one, it's certainly a change from the "what's the best xxxxx ?"-type threads that get posted. I do have a couple of comments that you may find useful/informative (or not

).
Betaplayer is very much a work in progress and is modelled more on WMP Mobile than a straight music player hence its separate playlist screen, as an example, how would mixed playlists containing both audio and video be handled?
I'm not sure what is causing GSPlayer to lose its settings as that has never happened to me, sorry I can't be more helpful here. The network browsing problems can be avoided to some extent by installing Resco File Explorer - a trial version is bundled with your Axim - and using it to map your network shares onto the X50 which works with nearly all applications. A big bonus is that network browsing continues to work even after the trial period expires as it's actually a hidden OS feature which Resco merely enables.
Don't you think you were a little harsh on MortPlayer? Maybe you didn't see the
skins page and assumed that the default interface was the only one available. As an example the attached screenshot is MortPlayer with the Media Jukebox skin running on top of a GPS display.