The font I use, IBM Plex Mono, I chose not because I love the font, but because it's the one I love most of the fonts with CJK variants (which basically means IBM Plex, Google Noto, or Adobe Source). It's unfortunate because I really like Libertinus (a rare serif monospace font), but trying to match different non-CJK and CJK fonts that work well together is annoying.

I wish it had my favorite in it so that I could do a blind test to see if it really is my favorite: https://juliamono.netlify.app

Sadly, IBM 3270 is missing from the lot. How can I write professional looking code that lasts a lifetime in anything less?

I also remember some nice ones designed to look like a smoothed VT-220 one.

Ubuntu Mono. I have been using JetBrains Mono for last 2 years and surprisingly I rejected it in a second iteration.

If you prefer proportional fonts, here's one that pads a 1/3 of a space before uppercase letters, so it makes camelCase more legible.

https://github.com/ericfortis/verdanacamel

Courier Prime won for me, I've always been a courier fan I guess because I wrote all my books in the 90s with it..

Fun. Interestingly the one that "won" for me isn't the one I normally use, which was one of the candidates, but I have used it a lot in the past.

Source Code Pro was my winner in this test. I use Iosevka on a regular base

Nothing comes close to Iosevka for me, after using it for a while it's hard to find the same mix of narrow+readable.

I already use Inconsolata but had customized it to a point where I didn't recognize it here. It won anyway. Validation!