I have a major in mathematical physics and mathematics and currently I'm on a graduate course in Physics working on a master's thesis. When I started the graduate course I was going to work on General Relativity and Quantum Field Theory on Curved Spacetimes (QFTCS). It turns out that by several problems, including the unfortunate that my advisor passed away, my thesis couldn't be on what I really wanted or anything related. Now it is being quite annoying to just work on something I don't have much interest and that doesn't seem to help on my future career, so I decided to study what I want on my free time. I have taken a one-semester graduate level course on QFT using Matthew Schwartz' book. The course basically covered scalar field quantization, vector field quantization, spinor fields, QED and renormalization applied to QED. I also have studied GR on my own, and furthermore, my current work involves GR, even though it is not mainly about it, so I feel comfortable with it. Now what I want to learn is QFT on curved spacetimes. The issue is that there are many different sources and many different approaches. I confess that due to my mathematical physics background I prefer more rigorous approaches, and talking about QFT on curved spacetimes I really liked the algebraic approach which my former advisor pointed me to. On the other hand, there are sources with a more traditional approach, and there are many different sources using the algebraic approach, so IMHO it is quite easy to get lost on it alone. What should I do? What resources should I use (I don't know which of them would be best for self-study)? What approach should I pick first? I believe it is good to know both approaches: the algebraic and the traditional. Since I'm feeling more comfortable with the algebraic, would it be better to start by it? How can I learn QFT on curved spacetimes on my own?