I am extremely biased toward IM too.
My experience is that FM is usually not strongly trained due to their attempt to do everything. Even if they go to unopposed institutions, they are not taken as seriously. OB/Gyn knows you won't be one of them, so you get limited exposure AND most places won't really hire you to do OB unless it's rural. If your inpatient is ran by IM, you won't be taken as seriously because they see you as the outpatient person. You do peds, and the exposure is usually quite poor because you're not rotating at real children's hospitals. There's also a lot of redundant rotations like ENT, surgery, ophtho, anesthesia, etc. that give you limited exposure.
On the other hand there's IM. You will be able to ignore all the OB and pediatrics. You are required to do 1/3 of your residency outpatient plus certain clinic hours, so you don't come behind to FM for the most part. I will say that usually FM does have stronger dermatology and procedures than your average IM, but if you're looking to become outpatient, you can focus your electives to cover this. Finally, there's fellowships. You can easily match Nephrology, ID, Hospice, and Geriatrics with board failures. Endo is possible but a bit harder. Finally, if you match at a place with in-house fellowships, you could end up doing better. For example, Valley Hospital in LV, NV is extremely easy to match IM with failures, and they have in-house PCCM and GI. You impress people there, and you can go from failed comlex 1 to GI doc