There have been a few threads about this, but none recently. I got the 300 dollar bose noise canceling headphones for step 1 prep and it was awesome. Needed the focus.
There have been a number of posts that say "bose is too expensive, you should get the GTX-P21410.b brand from xx1291lsa maker." I bet there are better deals than bose. I bet you can get a cheaper set that are better. I went with bose so i didn't have to do the research. 300 dollars next to the cost of medical school is negligble, you will continue to use the headphones for your pleasure, and, quite frankly, I did not want to waste my time (which was more valuable than my money) trying to find the better deal.
Bose is a respected name, great quality. Will you pay a little bit more than you should? Sure. Same with Sony. But you know what to expect and you won't be disappointed AND you don't have to waste time looking around.
Get electronic noise canceling rather than noise reduction (the ones that just block your ear canal) for prolonged comfort.
I paid 300 for my bose.