In undergrad I thought I wanted a PhD and was groomed to go to grad school. I now work at a lab at a teaching hospital, which has been great, since I have easy access to both research and clinical settings. While some familial circumstances heightened my interest in clinical care, I also realized that I wanted a much broader scientific knowledge base. Most labs, including mine, are entirely devoted to a single disease, or a couple of different pathways affecting that disease. I realized that while this in-depth understanding of one disease was great, I wanted to know more physiology, about more diseases, etc. I then realized that it was possible to do research and even eventually have my own lab as an MD. Granted, I'm sure this takes decades of hard work. And finally, it seemed odd to spend so much time researching a disease without ever interacting with or trying to treat patients with that disease. Overall it seems like MDs have way more doors open to them: purely clinical work, mostly clinical with a bit of research, or research with one a month in clinic. I'm not entirely sure what I want to do yet but I think I would be happiest with some combination of medicine and research. An MD seems to make sense for this.
I am lucky to have an amazing PI and wonderful PhD colleagues/mentors. Yet I'm fairly sure that my PI's lifestyle is not quite for me. As others have mentioned, a life chasing grant money sounds unpleasant. One postdoc told me that they regretted not going to medical school and becoming a doctor for a couple of reasons. First, in grad school you belong to one PI, and that PI can be a jerk, get recruited somewhere else, run out of money, etc. and you're completely screwed. Secondly, since you're basically free labor and your PI decides when you graduate, you might not graduate for awhile. On the other hand, in med school you have many, many mentors, all of whom want to see you graduate in four years and get into a good residency program because it makes the school look good. And at the end of that you can still do research! This is the opinion of one person, but it made sense to me.
That said, I have learned many important lessons in research that I think will serve me well in medical school (if I get in) and residency, namely how to deal with feeling like a failure every day at work, how to tell my PI that I made a stupid mistake, how to use organization and hard work to (partially) make up for a lack of knowledge, what makes a good/not good mentor, etc.