From my own understanding, and my understanding of dependent origination, ignorance is probably the root cause of all Dukkha. Ignorance causes unwise reaction and clinging, however there are different ways to focus on this chain of unwise reaction, if we develop more mindfulness then we may be able to see things more clearly and not react so quickly. Then we give ourselves the chance for some contemplation on whether it's beneficial or not, skillful or not, before just instinctively reacting. I think unwise reaction and clinging are more in the process and ignorance is the root cause. Clinging usually comes after unwise reaction because if we are not mindful we immediately react from our past conditioning and develop clinging, either negative or positive. But whenever we become aware that we are having Dukkha, we can investigate and try to let go of our clinging and unwise reaction.
It is also very helpful to work on our ignorance in the process, because it is ignorance that causes us to act unwisely. So I believe ignorance is the root cause, and the unwise reaction and clinging are more in the process. We can work in both ways to lessen Dukkha. First of all develop more awareness, so that we can be aware when the objects come in contact with our senses. Then we have a chance to not react so unwisely. We have a little bit of space in between the contact and the reaction, rather than continually just going quickly into it unwisely. Though if we have gone that far that we are clinging, then seeing the Dukkha of it and developing more Right View towards it, which helps lessen our ignorance at that time, is very helpful. We need to develop more awareness and effort. And helping to lessen the wrong view by contemplation works on the ignorance and the unwise reaction.