I have mixed thoughts on this..... Medical school overall seemed more taxing. I spent so much time in class and studying those first two years.... Third year sucked because you are the bottom of the totem pole, usually do not have a clue what the heck you are doing, and have to show up to everything eager and enthusiastic with a big fake smile on your face. 80 hour rule doesn't apply to students, so I spent some 100+ weeks in the hospital doing things I did not enjoy (surgery). 4th year was much 'easier' but stressful with applications to residency and such..
Intern year kind of sucks because again you know little about whats going on, you are the lowest level 'doctor' and are expected to do all the little things/BS. However, it was easier to remain eager as I knew I was where I wanted to be and was coming towards an end goal.
2nd and 3rd years were good, lots of learning, professional skills building, and doing what I love. Lots of work and lots of reading, but again did not feel bad since I cared about what I was doing.
4th year of residency was by far the best. You were 'the man' in the department, respected by nursing staff and your attendings, you knew what to do and could run things comfortably. Additionally I moonlit too much and had a boatload of money; had great friends and went on many awesome trips (Vegas, Cruise, Duck hunt, deer hunt, etc). Life was good...