I have extensive experience in basic science, and my honest advice is to avoid pure basic science, especially if you want a first-author paper. As you said, they are just much more time consuming. My current work is translational, and I have a very supportive group and advisor. I still do some bench work, but nothing as crazy as a full-fledged hardcore basic science project.
I will advise you start clinical research ASAP. Just manage your time well and be super efficient with studying. You can adjust your time commitment as you feel your bearings. Also aim to have a very productive summer between M1 and M2. From what I see, M3 might be the least productive for research. We had an M3 try to do some research, but rotations just ruined her efforts.