One of the things that really gets in the way of comprehension for me are typefaces with too much personality. These cutesy italics etc. really seem to affect my ability to get on with the job at hand.
This is why, despite trying, I've yet to find something that can outdo Consolas on Windows. I tried Fira this and that, Source code pro and a bunch of others from Google Fonts. They all are inferior to Consolas in my eyes. They'll either be missing the slotted '0', or look crowded in small sizes etc.