Better work on all interested groups of muscles every day or work on a part a day??
It depends on your goals and your level of training.
When you wanna lose it and get fit all over you should at least have one overall body session in your routine as complex movements (combination of working on different muscles with the same exercise) is very effective.
When you're already in a good fitness state and wanna push further or overcome a plateau you should think about going split workouts (this is only an example, you can also go HIIT). If you do 2-day up to 5-day-splits you need to be sure about your form (high risk of injury) and really push it to the absolute limits, it's useless or even dangerous when not.