It all depends on the client, his/her training regimen and any medical conditions that might be present (such as diabetes, kidney or pancreatic diseases, etc.). Personally, I would go for both protein and carbs. I don’t put much of weight at what drug using bodybuilders say, especially those who are sponsored by supplement companies. Again, a well-balanced diet plan is enough to provide all of those nutrients your body needs to recover and repaired its self from any type of workout.
I agree that combining both carb and protein post-workout are helpful and important. A lot depends on the type of workout. Carbs are especially important if the workout is a maximal effort cardiovascular workout to ensure adequate glycogen replenishment. Protein if the workout is a maximal effort resistance training workout.