Most difficult : Neurosurgery, Trauma surgery
Relatively Easier : Pathology
Easiest : Anatomy, Physiology (Basic teachers within Medical School)
Helps everywhere if you are the boss. The worst type is the juniormost.
An OB because they are often held up deliver someone else's baby.
It depends on you. For me, pediatrics would be sheer torture. So would most internal pills practices. Every day would drag on forever.
If I'm contained by the OR, time passes in the blink of an eye because I enjoy what I do. I may acquire some funky patients, but I can knock them out so they don't bother me.
With pretty much ANY medical specialty, you can find a situation that fits your needs. Some race like a solo practice, others a colossal group, others an academic appointment.
So the worst and best are dependent on the individual surrounded by question. I've see surgeons working hours that are just awful, but they love what they do, too.
Isn't it great that there's SOMEBODY for respectively different specialty?
Worst: Pediatric Oncology
Best: Dermatology, Dermatopathology