When it comes to in-car controls, you want to be able to use them without taking your eyes off the road. To this end, knobs that you can grasp for and feel the current setting are great. Knobs without a tactile indication of the current setting are OK, as you can find them without looking and only glance down to see that you are selecting the appropriate setting. Buttons are worse because you have to glance down to find them, but once you do you should be able to use them and know that the input was registered through the tactile feedback.

Touchscreens, on the other hand, are just bad for this. You have to look at them the entire time you're operating them, or else your hand might change position and not press what you intended to press. You also need to look at the screen to see that your press registered what you wanted to do. All of this looking at the screen means your eyes aren't on the road where they belong.