What is more effective: total body workout three or four times a week or training different body parts on different days of the week?
I am not sure if one is necessarily better than the other.... but they are different.
I am a huge fan of the overall body workout when I am hard-pressed for time. This also is great for weight loss and is a great way to train for overall fitness. When done at a good pace with no rest between sets, it really elevates the heart rate.
Where this type of workout falls short, however, is when people stick to one set of exercises per muscle group. For muscle hypertrophy (muscle enlargement), lifters need to overload their muscles. I personally feel that true gains in muscle mass come from different types of exercise for any given muscle group.
The more exercises we do, the better the neuromuscular response and the more muscle fibers are activated. Once we do that, we become stronger. When that occurs, we can lift more weight. Lifting more weight makes us bigger.
This being said, I prefer body splits for size because it allows lifters to be more thorough with each body part.
This does not mean you can't get bigger on a whole body workout. However, personally, I find it less effective.
Both workouts have their place. Just be mindful of what you are trying to accomplish so you can get the results you want.