My best in-class computing experience was probably in Systems 2, when we did the "hacking" labs. A lot of concepts around data security and code optimization started to make a lot more sense, and the problems were satisfying puzzles to solve. I was also fascinated by the idea of injecting code through a text box, and gained more appreciation for cybersecurity.
My favorite outside-of-class computing experience was when I figured out a way to make non-euclidean spaces in Unity 3D. There wasn't a whole lot of documentation on this around the time, so I had to figure everything out from scratch. Basically, I wanted to make a Tardis (from Dr. Who) that was bigger on the inside, and allow the played to seamlessly enter/exit the space. I learned a lot about how spaces are rendered, and the project was a success!