What are the important factors to consider when choosing a Master topic?
One thing to keep uppermost in your mind - the topic of your Master's thesis is not necessarily the one that you have to pursue in later research, such as part of a PhD.

The point of a Master's thesis is to demonstrate your ability to do research. Opinions might vary on whether it is a reasonable expectation that the research that you do for a Master's thesis has to be world-class and leads to one or more publications. In my view, it would be nice, but it isn't a requirement.

What you need to get out of your Master's thesis is a strong demonstration that you are capable of academic research. You decision on which supervisor and topic to choose should be guided by this driver. 

Pursuing a research topic merely because the professor is world-renown may be misguided. What happens if you don't strike up a good working relationship and your research falters because of it? Will your professor's reputation outweigh a mediocre research effort?

Your drive and interest in a research topic are strong factors of whether you will succeed. The motivation should come from you - most of the time - to address your research topic. Again, if you aren't particularly interested in the topic, you are going to find it hard to keep going at it when - and it is a matter of when - the going gets tough.

I reiterate that at the end of your Master's thesis, you want to demonstrate your research ability. You are still learning the skills and craft of research, and for that reason, you want to seek teachers who are skilled at teaching how to research. Is it necessarily true that the best practitioners of science research are the best teachers of how to do research? Sometimes true, sometimes not.