What I remember most in general from my undergrad courses is that most the "fun" ones are the ones where I already was interested in the topic to the degree I k

What I remember most in general from my undergrad courses is that most the "fun" ones are the ones where I already was interested in the topic to the degree I knew something about it or if I didn't it's obvious I would have learned something if it was brought up at some time. The "not fun" ones on the other hand are the ones I remember the most from because those memories aren't competing with lots of other exposure to those concepts and thus they left a lasting impression that I might not have gotten any other way. Going down the path of "fun" might be easiest and overall more enjoyable, but it also ultimately might be less fulfilling in the end. Your mileage may vary, of course.