Maths.
Requires the least work and least effort relative to my other subjects. It's the subject with the most relaxed lectures -- we listen to music, eat and drink coffee. We turn up 15mins late and then the lecturer comes in 5 minutes later too which is great!
After we learn the concepts we just chat, have paper ball fights, paper-plane flying competitions etc.
For me, it's also the most intellectually interesting subject I am studying. We often talk about philosophical implications of some mathematical laws/concepts with the lecturers and show real-life uses of what we learn.