• proper adblocking with AdAway
• ability to patch official apps to remove ads and improve the usability with ReVanced
• being able to root the device and use HttpToolkit to analyze the data that flows from apps to the web
• extensive customization (I can choose my own launcher and keyboard application)
• proper file management, especially with Total Commander
• watching Dolby Vision .mkv files with mpv
• price (iPhones are all way too expensive)
• Apple's stance against repairability

And this point is more hardware-related, but I've started to really love my Nothing Phone and its LED lights on the back, which produces amazing photos because the light is much softer than the small flash used by other phones. There isn't a single Apple device with a feature like this. You could probably get a case, but it's nice to have this integrated into the phone.