Which is better for music: usb, aux or bluetooth?

I'm going to get an aftermarket car stereo for my car. I have an iphone 5 and i want to know which source has the best quality for the music.

Personally I would make sure that it offered me both the 'aux' and bluetooth…

Depending on what how you store your music… You might find the USB more convenient - just plug a flash drive with a couple of hundred tracks stored on it and press play.

I use 'Bluetooth' and reckon the quality is pretty decent… Just be careful though - in normal circumstances I might advise someone to avoid the bluetooth option - it's convenient - the quality from an 'aux' or USB source should - should beat it.