The most useful goal is arguably to become a subspecialist in a particular field within pathology, for which you can be a go-to person when other pathologists need help, and at the same time maintaining basic skills in handling general pathology, at least for the most common conditions where you are expected to practice. In either case, it is important to be able to extend beyond your comfort zone when needed, and at least try to solve cases that fall outside the official subspecialties of the pathologists at hand, even if you may need to search for someone to consult you for the case.
Judge subspecialties primarily by their presumed everyday work, and how well it fits with your personal strengths and weaknesses. As much as possible, base your evaluation on real life exposure to the practice, and put only minimal weight on how interesting the theoretical literature thereof is.
To some degree, consider whether you will want to live and work in (or commute to) a larger city (with more demand to dedicate yourself to a narrow-scoped subspecialty), or a relatively smaller town (with an increased demand for broader or otherwise generally needed subspecialties, mainly surgical pathology and cytopathology but mostly also hematopathology).