This is a very tough question to answer. First of all you should have a goal in your mind what you would like to become? Most people usually have a goal in their mind, like they would like to become an electrical engineer, or computer scientist or engineer, doctor, aeronautical engineer, etc. Based on that decision and pickup a field. You should have an interest in a specific field. Having an interest in becoming something or landing in a specific career will help you boost energy and you will most probably put lot of efforts and hardwork during your coursework. I would also reiterate that some of the coursework in such fields are difficult or challenging. But your goals and interest will help your tackle such hurdles.
In my opinion it does not matter if a field is STEM or not. If you like what you want to become most probably you will be successful. Do not force yourself to just be in a STEM field, instead look for what you want to become.
I would also suggest you to also go through some websites like salary.com and have atleast an approximate idea about how much companies usually pay in a specific sector.