That's a quandary, to be sure! To be honest, I am not an Apple person but will do my very best to leave my biases out of it!
Both phones will run a smooth and clean OS - the Pixel 4 is stock Android and iOS has always been a bare-bones-and-it-works OS. Both cameras are supposed to be phenomenal but I thought I read in one of (AC's?) comparisons that the 11's camera performs better in lowlight. But really, they will both get the job done and get it done well.
Both are probably going to be pricy... And both of them will be great!
Since they are so close in features and OS as far as smoothness goes, what is more important to you? Would you prefer going to Apple and having to get all Apple products; or having to get Pixel stuff but still having some flexibility with accessories for the Pixel 4? What phone do you imagine yourself looking at, picking up, and using for the next year or two?
It's a tough choice - let us know what you decide!