I listen to my local radio stations, so I don't need to pick songs to listen to on my computer, and I can focus more on studying rather than switching songs to listen to on my PC.
When I used to study for exams and also for college, I would always choose to listen to the music that I enjoyed at the time. I would usually either have an album that I would listen to or I would listen to music on the PC that I had as well with the songs I enjoyed the most.