GoKawiilWireless CarPlay is the most convenient option for most people. You don't even have to get your iPhone out of your pocket for your car to connect and start playing your favorite songs. Unfortunately, it isn't the best option for those who demand the best music quality.
Take it from Apple: wired is best for your music. Apple's guidelines for Apple Music through CarPlay confirm that only a wired USB connection will allow you to play lossless audio. Lossless audio is compressed without throwing away any of the original audio data, meaning you're not losing detail. A wired connection means you can switch to lossless streams, as long as you have an active Apple Music subscription and have enabled this option.
Technically, it's all down to the codec. Apple uses LPCM for audio on wired CarPlay connections, but switches to AAC-LC when using wireless CarPlay. LPCM carries uncompressed digital audio, so a lossless ALAC track from Apple Music can be passed to your car without lossy compression. Wireless CarPlay has to encode the audio into AAC-LC first, using lossy compression to reduce the bitrate and discarding some of the original audio data in the process.
The end result is lower-quality audio, but that doesn't mean wireless CarPlay automatically sounds bad. Whether you hear the difference will depend on your car's sound system and your ears. The speakers and amp (if your car has one) have a huge influence here. Plus, other distractions, like road noise, are never going to provide the perfect environment for listening to music.