I use USB for my music. I don't want to pay for any kind of subscription service, and cell phone service is not available everywhere I live. Also, playing from the phone has issues such as playback not resuming where it left off on restart or after a phone call (which doesn't work well for audio books).
I was having many problems with USB, including UConnect intermittently not recognizing the drive. Most of my USB playing glitches have gone away since I fixed the encoding errors of my MP3 files (almost 4000). My UConnect glitches reduced to 10% or less of what they were. (I used mp3val and ffmpeg to fix the MP3 errors. Both are available for Windows and Linux.)