Choosing the design area that is easiest to do is akin to choosing the design area that you're most passionate about. This will differ from person to person. For example, my presentation 1 was on environmental design and presentation 2 was on communication design. I'm far more passionate about architecture than I am about graphic design, so while I put a lot more hours into presentation 1 compared to presentation 2, presentation 2 felt like more of a slog.
If you're ambivalent or equally passionate about the three areas, start looking for a problem that you want to solve with your design, or an idea that you want to realise. As long as you do something that excites you and motivates you, the project will seem 'easy' (even if you have to pull a couple all nighters during the term breaks).