Any answer to that question would be very subjective. The various music players have pros & cons including functionality, price & size. After trying many different music player apps, I've settled on TuneWiki (which is free) because it has so much functionality. TuneWiki:
- Plays songs (MP3s, WMAs, etc) that you've downloaded to your Android Device.
- Streams Internet radio stations and videos.
- Displays synchronized lyrics. (Very nice to have sometimes.)
- Does LastFM scrobbling.
- Song ID. It listens & identifies songs that are playing in the room (like Sound Hound but you can't sing or hum to it like Sound Hound).
- It has a pretty nice, intuitive UI.
- Does music social networking/mapping stuff. (Not that I care.)
- Misc. other stuff.
I also use Pandora to kinda "build my own radio stations" and stream them.