I am only a med student but if you are asking about EM vs. anesthesia, then maybe you are a med student trying to decide like me. If you are, I have a third option or consideration. One reason people like EM is because you are a "jack of all trades." But FM is a "jack of all trades" too (except for the acute stuff but that might not be so fun when you are older according to what some people are saying here).
EM
1. Make more money ($350k+)
2. But for a shorter period of time until you burn out it seems in your 50's (or work less shifts or switch to something like UC making a lot less)
3. Your schedule is more erratic (nights, holidays)
4. You are dependent on hospital contracts and politics from what I understand
FM
1. You make a lot less money ($250k average)
2. But it is consistent because you can work until the day you die (80's) if you want, that's 20+ years of working (if you want career longevity) than when you are likely to burn out in EM (assuming people are right about burn out and burn out rates)
3. You are in even more demand than EM almost anywhere you want to work in the US (you can start your own practice or join others almost anywhere if you are business minded, don't need the ER/hospital)
4. You have a more regular and controlled schedule and can set your hours with your practice
5. You don't have to fight with drunks or see the worst of society (usually)
6. Outpatient medicine usually offers a better lifestyle
7. In most places you can still be your own boss and independent from hospitals and all the politics and worries there, this is huge
8. You don't have to fight with specialists to get them to see a patient or admit them, specialists depend on you for a lot of their patients
9. Or if you want more money, you can be an FM hospitalist in a lot of places, make $300k+ for a while, then switch to outpatient FM when you get tired of hospitals and hospital politics
10. FM has its downsides for sure (e.g. insurance companies, paper work), but I don't think it's a bad gig depending on what you want, and too many med students (including me) sell it short, but having said that I would probably still pick anesthesia over FM or EM 😉