Audio quality question: data cable vs headphone jack

I want a new headunit for my car, but I'd like to know how much difference, if any, there is between the data cable and the headphone jack.

I currently have the data cable adapter on my Kenwood, but it doesn't allow me FULL control of the music. And I tried the headphone jack on my mom's CR-V and I liked that I could hear phone conversations over the car speakers. I really want the benefit of calls on the car speakers, but I don't want to sacrifice music quality if I don't have to.

Any and all help is greatly appreciated.