2. Personal Risk. How much you and your health and safety are compromised by the performance of your work. This could encompass anything from dealing with extremes of physical demands to working odd shifts and all hours. Or working outside vs inside.

3. Stress Levels. This is a concrete and serious aspect of a job. If you are working as a producer in Network live television; your stress level will be considerably higher than if you are selling real estate.

4. Level of Dedication required to perform your work. Say you are a Preist and must comfort the sick and dying regularly; you had better be dedicated.

I use these four very broad outlines but inside each proscription is numerous and finely judged aspects of work.
So as an example I would offer the job of Coast Guard Search and rescue. This has to be in the running for most difficult and demanding.
Or maybe high tension powerline repair. Undercover narcotics agent. Small list; it would be interesting to see if anyone has anything to add.
Then there could be a category for everyday jobs like Policeman or Architect. I hear the Architect requirements are much more demanding than taking the LSAT'S or the CPA exam.
Even office work could have it's difficulty rating; or even tech work.