[grayclhn]

I like

    \usepackage[osf]{sourcecodepro}

It might be idiosyncratic preferences, but I like the height variation in monospace letters.

You might also want to use

    \DisableLigatures{family = tt*}

from the microtype package. It doesn't normally matter, but the sourcecodepro package has an "fl" ligature that's usually unwelcome.

[edwintorok]

Thanks, I'll use the \DisableLigatures. I actually don't like old-style numbers (see the [lf] option for Fira), but its a matter of personal preference.