I know to some extent the aux in audio quality will depend on the player, but if you play music through a car stereo via bluetooth and via aux/line in (say from an mp3 player), which will sound better?
Even though mp3 is compressed, it is decompressed at playback.
There are those that will say that Bluetooth will sound the same as aux/line in, and under good conditions it does. Bluetooth is however wireless technology and just like anything wireless it is subject to interference from anything that operates on a simular, or close to same bandwidth. Ever used a Bluetooth headset and got static in it? The same can happen in your car, so I think Aux/Line input is the better way to go if all you want is to get the audio from your device to the stereo. It is usually the least expensive also.
Even though mp3 is compressed, it is decompressed at playback.
There are those that will say that Bluetooth will sound the same as aux/line in, and under good conditions it does. Bluetooth is however wireless technology and just like anything wireless it is subject to interference from anything that operates on a simular, or close to same bandwidth. Ever used a Bluetooth headset and got static in it? The same can happen in your car, so I think Aux/Line input is the better way to go if all you want is to get the audio from your device to the stereo. It is usually the least expensive also.