Personally speaking, I would love to switch to Firefox just to use uBlock Origin, but this picture[1] shows Opera's killer feature.

It's a screenshot of today's old.reddit.com/r/all. You can see how you're able to read all of the text vertically, without having to scroll sideways, because it wraps perfectly to the current pinched zoom level. No other browser works this good on Android, and reading stuff is my main internet use case. Try seeing how that website looks on any other browser, it's ridiculous how unusable they are.

[1] https://files.catbox.moe/5t853c.png