This problem has been driving me crazy for the last few weeks. It actually got worse with the update from iOS 7.03 to 7.04. (Before, eventually, the sync would finish correctly after several attempts. Not anymore.)
The ONLY thing that worked for me was to connect the phone to my iMac, and in iTunes, select the phone; go to "music" and deselect the button to sync the "entire music library." Select the button for selected playlists, artists, etc. I checked to include music videos, etc. Then I manually selected ALL of my playlists and ALL of my artists, etc. When I clicked to sync, it worked! Took a loong time, but I could see it happening on iTunes and on my phone.
What a pain! C'mon Apple! Fix this one!