I'm in the rare position of having in the household 2 generations of the same car, both highly specced, one with conventional controls and one with touchscreen.
The screen has greater functionality in the sense that you can play your music through it, it incorporates the sat nav, even web surfing, etc. On the other hand, a lot of that functionality is guff - who on earth needs their text messages read aloud to them by the car while they're driving?
Without a doubt the older car with conventional controls is easier, simpler, and less distracting to use. There is absolutely no doubt whatsoever about that. None. Changing fan speed requires a turn of a knob. Activating wipers requires an instinctive nudge of the index finger. Both of these things - and much more - can be done instantly and then forgotten about, without any need to take eyes and attention from the road. The same functions on a touchscreen both take longer, but also require the driver to loom at something other than the road ahead. Dress it up any way you like, but placing critical function on a touchscreen and, even worse, burying them several menus down is a triumph if technology over common sense.