This is an interesting question. I do not know if you can say it is one or the other. It is really a combination of both.
On the one hand management is a science, because whatever you are managing is like a machine. Therefore, if you study the machine in careful ways, then you will be able to see what could make it more efficient. And with prolonged study and examination, you will be able to make everything better. You will also be able to take out what is not necessary.
On the other hand, it is an art, because you are dealing with people. All people are different and even the same person has good and bad days. So, to deal with them takes creativity and sensitivity.
Finally, artistic creativity can also enable a good manager to think outside the box, which can offer innovative solutions.