I wouldn't suggest you base it solely on what you excel at, focus on what you like or want (which are basically the same thing). I can't really help with this kind of trouble as I've always (since I started thinking about what I wanted to do) felt attracted towards a mix of computer science (specially programming) and astronomy.
But what I would recommend is focusing on what you like to do, more than what you're good at (although they can be the same). Even if you suck at something but like it, you choose it over something else because you will get experience at whatever that is and eventually become good. Those tests that tell you what you suggestions based on questions are helpful when you have completely no idea what you want to be, but don't take them that seriously, those sites also have a lot of information and lists on various jobs so I would suggest looking at those as a start.
Once you have an idea of what you want to study I suggest you look into places that teach them and what do you need to enter. How much the program costs could also ultimately affect what you choose.