Whichever is more useful to you in this moment. If the answer is both, start with the easiest one first. Once the habit is built you will be ready for the more challenging task.
I think it works for both, creative tasks need focus too. You can choose in what you want to apply this but any task that you need to complete would work. I suppose the important thing on set deep work time frames is to start building your focus (to be more time wihtout distractions) and mindfulness (to realize sooner when you have a distraction and be able to return to concentrate)
If it's the weekend then it's a creative/productive task depening on my to-do list. If it's a weekday, then it's focusing on my work.
It surely has stop be creative because we always spend time for others. Like working,living and more and more effort others. So during this deep work time,at least you have to try to live for yourself. So try to live during this time for yourself.