A lot of things can be said about how to pick a topic for a Master's in mathematics or any other subject. But a few general things could be pointed out.
First: If you are thinking about doing a Ph.D., then you have to find a topic that interests you. You do not want to pick a topic that you hate just because it might increase your chances of getting a job. If you do so, how are you going to find the motivation to study hard all those long hours required when doing research?
Second: The list you give of things that you are interested in sounds like you might want to consider applied mathematics. If you are interested in finance, you might consider do a degree in that area instead of in mathematics.
Third: While picking a topic that you are interested in is important, it is not bad to consider what might actually land you a job. What I would recommend you do is to look up job descriptions. If you are in the US you could go to https://www.usajobs.gov/ and search mathematics. Then you can get a feel for what the government is looking for. You could also look up websites for various companies and search for job descriptions.
Forth: When you look for an advisor, one of the most important things you should look for is someone you can talk to. You want to have a relationship with your advisor. How much is your advisor for example available? One thing I strongly recommend is to set up appointments with several professors and just ask them what they do and if they would be willing to do a project with you. Talk a bit about your interests and ask them if they have ideas for topics. The purpose of such a meeting is, of course, to get a feel for what the professor does, topic wise, but it is also about seeing how the person communicates.
I hope this helps a bit.