I find they're both pretty crap and playing a browsing songs is a tough effort (specially when errm pulling over to change the song... wouldn't use my phone while driving )
I dunno about WP but for Win8 I would recommend Music Info. Music Info for Windows 8 brings your collection to life | Windows Phone Central
Its the same dev that made Artist Info for WP. It looks awesome but its not really a better player sadly.
I dont think there are APIs available to build a competetive musicplayer on WP, yet.
Lets pretend I'm using Windows XP, and I hate Windows Media Player so I switch to an alternative like VLC or Media Player Classic. Now for my WP8, I hate the xbox music app, it there another?
For the time being no. Xbox Music is cooked into the OS. Can't even uninstall it. All we can really hope for right now is updates that bring it closer to Zune.