Well, this is something that comes up a lot...let me give my opinion. If you *know* that you want to do primary care, then Family Medicine is probably the best option. (I say this as a first-year FP intern.) We have a fair amount more clinic time during residency, and get much more experience dealing with everyday type stuff. On the other hand, if you want to specialize, and like the careful investigation of disease, and if you know you don't want to work with kids or pregnant women, then go IM.
Having said that, many IM's make great primary care docs for adults, and many FP's spend a lot of time on complicated hospital patients. As an FP you are kind of limited after residency...if you suddenly decide you want to be a cardiologist, you're basically out of luck. On the other hand IM's have the limitation of little or no training with kids and no possibilities in OB. There is a little bit of further difference in the philosophies of the specialties...FP is perhaps more holistic and open to alternative medicine, while IM is stronger in basic science. But either way your philosophy is what you make it...I'm an FP, but I tend to have a more scientific bent and am suspicious of most alternative medicine.
Really, you should probably make your decision on what kinds of people and diseases you like to deal with (kids, adults, cardiac, renal, etc.).
