I've found source code sans to be an excellent font for LaTeX, and the companion source code pro for code blocks. They are significantly more readable to me and to most people I know, though that may have to do with screens being much higher-resolution than when computer modern was created.
Here's my arm-chair hypothesis: the thin connecting lines (don't know the technical font term, though I'm sure one exists) showed up fine on low-res screens because they simply couldn't be made thinner than a certain amount. On high-res screens, they get much thinner, and my eyes have trouble tracking them. Easier to read on paper, though.
The technical term is "hairline," though that tends to get used primarily in fonts that have high stroke contrast, of which Computer Modern is most definitely an example.