I cannot stand dark themes. They have always bothered me. I normally prefer bright themes over dark themes. Personally, my favorite themes are neutral though.
I quite like both. I think which is better in my opinion depends more on the type of forum. Gaming forums tend to suit a dark style better in my opinion while support forums/ business forum forums for example suit lighter styles.
Only very few specific niche would be suitable with darker themes, mostly it should be bright so it does provide ease to the viewers, dark themes are sometimes very hard on the eye for some.
As long as its done well, I prefer darker themes. Same goes for light I guess, but the best dark theme beats the best light theme hands down in my book.
Bright themes like this forum are my favourite. I know some people prefer dark themes but I find it hard on the eyes. Some forums even have multiple themes for you to choose which is awesome!
It actually depends on what your website or blog is about. If it's about gaming, adult or bets, I'd go with dark ones. If it's something relating to health, information or fansites, I opt for lighter colors.
Depending upon my mood I prefer sometimes bright and sometimes darker themes . But mostly medium which is neither too darker nor very lighter suits my eyes.
I prefer to see the bright theme. I think it is easier to read using that theme and prevent myself from getting an eyestrain. My eyes need to relax from the high contrasting graphics and background design and stay away from headache