I have not tried out iphone 11 or pixel 4 but I am currently using pixel 3. So thought I can give some feedback about Pixel 3. The camera is definitely the best phone camera I have ever used. It's not just about the camera itself but also the AI which enhances the photo quality/fixes the colour etc. It's specifically good at fetching lights: sunrise, sunset, sky, even moon and fireworks.
As far as I know from my friends, iPhone is not very good at the making photos, not bad, but not that good.
Oppo does make good photos, but not so good in other features.