Personally, I find myself gravitating towards light themes. I know, unpopular choice. I use a dark theme as well, but I find a lot of dark theme plugins to be difficult to read. I used Darcula for Android Studio for the longest time because I felt like a hacker. Over time, I found comments and certain colors hard to see on a dark background. Now, I notice that at times looking up from a dark screen into a well-lit room actually hurts my eyes. I don't seem to have as much of a problem with a lighter theme. I make a few tweaks to the font size and font type to make reading a bit easier.
I also use a cool plugin called Night Shift (available on Chrome and Firefox), which I have customized to dim my screen in the evening so the brightness of a lighter background isn't as hard on my eyes. However, if the theme looks cool, I will try just about anything.
I am curious to know if any of you are light side or the dark side!

I agree. When I have dark themes enabled I can stare at my screen longer, but that ends up causing me more eye strain. A brighter screen reminds me to lift my head up and rest for a bit. This isn't to say I still won't use a dark theme, but I use them more infrequently.

I like dark themes, but I think a lot of sites are too dark. Light text on a background that is too dark is really hard to read, the contrast is just too much for me. Usually, I wouldn't make the background much darker than about #666666, dark enough to be a "dark background", but light enough to not cause me eye strain.

Dark. It's easier on my eyes most of the time. Most of the issue for me is avoiding 'perfect' contrast that you see in many light themes (black text on a white background, or something similar with a WCAG contrast ration near or above 19.0), and I find it much easier to find dark themes that are both lower contrast (I usually aim for something like 15 or so) and not particularly hard to read.

DEV's is reasonably good IMO (though I would prefer if it were more of a neutral or warm gray over the blue it uses), but some (Windows and Android, I'm looking at you) are just as bad or worse for me than black text on a white background.