I'd pick Dark mode for eye comfort, but have you considered users who work in bright environments and might prefer light mode for that reason?

I'm curious, what kind of app are you building? The answer might depend on the specific use case and user demographics.

I'd pick Light mode for better readability, but have you considered users who primarily use your app in bright environments like outdoors or well-lit offices?

I'd pick 'System default to let users decide' - users often have their own preference set at the OS level and forcing an app mode can be jarring.