This question was asked on Quora. When I see the question, I set my mind to answer the question. I know I have a little experience on this section but I have tried my level best. Please never forget to mention if I miss anything or make any wrong. By the way, the answer of this question should be aim depended. Please let me explain.
You will find that most of the Python Web Developing companies are using Django. Obviously they get maximum benefits from it like easy or resourceful. Whatever, as Django is preferred by them, you may have to go with them to get a job.
Till now, I have never found a company who are working on Flask only. If you find me please never forget to share. (Here I wanna add that some companies are developing APIs on Flask. But their major project is on Django.)
I believe that different projects may need different frameworks. If the project is small, then you can use Flask. As you don't need extra thing that Django provides. Yeah, off course, you can extend Flask to the level of Django using extensions and following MTV pattern. It’s a charming feature of Flask.
It's an another great things. Programming on Python is my hobby, also now I wanna build up my career on it. I like micro-frameworks, so I prefer Flask to Django. Actually, when I started with Django I found it too much hard to learn. So I moved to Flask being disappointed. Oh! I am happy now as I have learned all basic things of a web framework. After that, I have made some projects on it like URL Shortener and Blog Engine.
Now I am moving back to Django. But this time I get it easier as I have learnt Flask well. I need to be expert in it to get a job. Not only that, I am in love with it. When you will discover how charming the Django is, you will just love it. What I wanna say, You can try my procedures.