Surgeons have to know the most to do their job well.
Med students and pre-meds posting here may not realize it yet, but surgeons actually do have to understand all the medical physiology behind the disease processes. Surgeons actually do make diagnoses, often when the EM and IM docs can't quite figure out what's going on, they call the surgeon - for abdominal things, vascular problems, endocrine issues that could be treated surgically, all sorts of things.
Spend a month on a surgical service with ICU patients... you will see just how much critical care management every surgeon can handle - surgery residents learn early on vent managment, how to manage fluid balance and hypo or hypertensive problems, run drips - plus they are easily the best at any critical care procedures - central lines, art lines, swans, chest tubes. Rarely will a surgeon call a consult for a critical care patient except maybe a nephrologist just b/c that's who actually gets to say a patient needs dialysis (and we already know the patient needs dialysis before we call them). Surgeons are also trained to do endoscopy, which means they can do all the GI docs do (except not usually ercp), and also operate on the patient's problems too.
Doing surgery is actually quite a fine craft to learn itself, so this takes some smarts too. Learning what to do when a case does not present like the textbook (which happens quite often), takes some quick thinking on your feet and knowlege from lots of background reading you've hopefully done about similar rare cases others may have described.
This is why we spend 80 hours a week all 5 years learning our craft...how can you say a neurologist who spends less than 40 hours a week is smarter - they sure do know more about Parkinson's disease and that sort of thing...but not much about any non-neurologic disease.
With few exception (like a clear-cut MI or CVA), if you ask me to pick one doctor to take care of me when I present to the hospital really really sick with multisystem problems, I would definitely say a surgeon.