I think a lot of these fonts deserve a little blurb about their history and purpose. For example Liberation Mono (version 2+) and Cousine are fundamentally the same font available under the same SIL Open Font License https://en.wikipedia.org/wiki/Liberation_fonts#Distribution

Personally I use and recommend Liberation Mono / Cousine at 9pt / 12px. I've been using this font for years so it's just ended up what I'm the most comfortable with for both reading and writing.