I can't give you an "expert" opinion, just an opinion of dubious value. There have also been a few threads kinda sorta addressing this over the years.
PhD: highly focused, generally only work in that very specific field, could run a hospital microbiology lab but has to have MD oversight/medical director somewhere up the chain and has essentially zero authority outside of that one lab, generally paid less unless also have a research income but may also outcompete a focused MD-pathology microbiologist for the same reason. Good ones learn enough about patient care to be helpful, bad ones bring in questionable tests of unclear value and don't answer the questions clinicians most need answered -- i.e., they don't have a clue about the practice of medicine and never work to overcome that.
MD: more involvement in other pathology specialties, ability (often expectation) to oversee not just the microbiology lab but also other labs within the pathology department, takes longer and costs more to get the degree plus residency plus fellowship, can generally expect to be better paid than a focused PhD. The good ones stay involved in the lab rather than simply letting the senior techs own the show but otherwise already have a reasonable grasp of what is clinically important, while the bad ones just don't know or care how the lab is running and spend all day at lunch/golfing/surfing the internet.
Personally, the "best" are the more broadly trained M.D.'s who take the time to stay involved in the day-to-day activities of the lab without getting in the way of the workflow. But there are some very good PhD medical lab folk too, mainly those who, like good M.D.'s, don't prance around declaring their degree & training to be the end-all-be-all of the universe and take the time to listen to and work with their clinicians and their techs.
