This topic has been discussed before; you should check out the research FAQs as RxnMan suggested. FWIW, I agree with the others that choosing an appropriate PI is infinitely more important than anything else. You are unlikely to spend the rest of your life doing the same type of work you did for your PhD anyway. So your main concerns should be to find a PI who makes training students (and graduating them in a reasonable amount of time!) a priority; and picking a lab that will give you strong general training in scientific thinking. The specifics of your project probably won't matter twenty years from now, but the process of completing that project and learning to become a scientist will stay with you for a lifetime. Picking the right mentor will help all along the way when you need LORs for post docs, introductions for jobs, someone to help you troubleshoot when projects aren't going right, etc.
Edit: BTW, it's impossible to know until you get on the wards whether you will like clinical medicine and/or be good at it, so I wouldn't worry about people telling you that you wouldn't be a great doctor. Likewise with getting into the lab and becoming an independent scientist. It takes so many years to develop yourself into either a physician or a scientist that there is certainly time along the way for you to discover and develop whatever talents you possess. There are bound to be some strengths that you have in both medicine and science; as a second-year med student who has yet to start your PhD, you just haven't had enough lab or clinical experience to figure out what they are yet. Best of luck. 🙂