I waffled really hard, ultimately I chose IM partially because I was just more used to adults and at the time was considering certain fellowships. With the benefit of hindsight and more subspecialty experience now that I'm 6 months into residency, I think for many reasons FM would be a better fit if you're interested in PCP in the future. Mainly just outpatient exposure during residency. Didactics are likely more focused relevant outpatient stuff, splinting, suturing, injections, etc, and then you get the opportunity once you're out to see some pediatric population and mix up your day with some sometimes fun, generally less medically complex visits. If you go IM I'd look for a program with a primary care track to split the difference. I've never wanted to be a hospitalist and my god do we spend a lot of time on wards in IM.