Over the years I have studied a lot of subjects and attended a lot of classes, so there have been many subjects that I would say that I enjoyed studying (English being one of those hahah). But if I have to choose one, I would go with Organic Chemistry. Study different types of chemical compounds, how to synthesize them, performed practice activities in the laboratory, use chemistry reagents, and so on... When I remember all the things that I have learned about Organic Chemistry I can say, for sure, that I enjoyed studying it. However, some things kind of "ruined the experience" a bit for me, for example, the tests and the exceeding amount of time that I had to study in order to achieve good marks.
It is kind of funny because before I studied Organic Chemistry I knew very little about it, so I didn´t know what I was facing, but looking back to it, I am happy, because I can say that, finally I enjoyed studying it.