This is all observational on my part so take it with a grain of salt. Although I have some experience in the field there are so many needs in different areas that my opinions come only from my experiences.
That said, if you are working relatively independently, it may be of more value to have a broad base of knowledge and to be able to operate within the resources you have available. Thus generalists are typically of more value in very underserved areas and specialists in shorter trips to provide services (I.e. cleft lip/palate repair, eye surgery, dental work, etc.) OR in larger hospitals acting more in a training capacity (which is a huge need internationally). Honestly very similar to observable differences between rural USA and urban USA but possibly with less resources/help, more advanced pathology, and more patients internationally. But all depends on where you go also.
I spent a bit of time in the mission field prior to medical school in Asia and the Middle East. In both places I was literally anything would be valuable, BUT a generalist seemed to be the most versatile. Thus most American physicians I worked with were FM trained but operating at an extremely high level after training at hubs in other mission areas with GS, OB/Gyn, anesthesia, etc. but like I said all of the above would be valuable in their own way, and if they’re comfortable doing some general medical work even better. My thought in school has been FM, GS, EM, IM/Peds, OB/Gyn are the most valuable fields. But FM took the cake for me being a strong mix of outpatient/inpatient medicine in training, having OB training (which varies greatly program to program), having a decent amount of procedural training, and seeming to be the most frequent field I encountered on missions - like a strong foundation.
There is a great film called “The Heart of Nuba” about one such FM doc in South Sudan. Recommend it.
All that said, most of these FM docs are not doing major surgery (the one above excepted, and he for good reasons. There are others of course in similar situations). Many do epidural anesthesia and C-sections, but that’s probably the limit. So if you like surgery then it would be much better to go GS. EM I feel could be of similar utility as FM but possibly in more high acuity areas or disaster relief situations. Anesthesia would be very helpful as long as you have surgeons to work with (I know that’s not all anesthesia does, but that would still be the greatest need). In bigger hospitals OB/Gyn services (especially OB) can be EXTREMELY helpful. Just depends on your interests and where you wanna go.
Long story short, if you wanna be in remote areas providing services long term, I would recommend FM or maybe IM/Peds. If you wanna travel a lot between bigger areas and remote areas or stay in bigger areas, then the above + GS/anesthesia/EM/OBGyn sound good. If you wanna do short term missions or do training/teaching, any specialty would work - with emphasis on services that are hard to come by - Ophtho, NS, Plastics, etc.
If you are interested I can privately share with you info about FM residencies that emphasize this type of work. Also would be happy to provide more specific insight from my own experience privately.
