After using the F807 for a few days, I'm finding I still haven't settled on one music player. I'd rate the default player and Neutron as having very good sound. Neutron seems to edge out the default player in UI for me (once you learn it's quirks), as the default player is functional, useable, but a little bland (and missing my album art! -- still need to investigate).
PowerAmp seems to beat both on features and useability, but it doesn't seem to sound as good (each player has flat or no EQ set). Without knowing how to describe it better, I'll just say that PowerAmp sounds "vanilla" or "bland" in comparison.
The reason I haven't settled on Neutron yet is that I've found that on at least one track, with my Westone 4 using headphone out, the track is unpleasantly distorted -- which doesn't happen at same place/volume on other players. It has to be something the player is doing but I wouldn't know how to figure out how to resolve it.
Anyone else still switching between players or have you settled on one (and why)?