The Pixel 3 is a big improvement over every other Android experience I've had, and I've been in the ecosystem since the Nexus One. It's the first Android phone I've used which actually feels like a premium phone, which is what I'd expect, considering its hefty price tag. Its camera has been called the top of the line by many reviewers. Heck, right now there's a post in the HN front page about the Pixel 3's camera [0].
Stock Android is still kinda buggy and rough around the edges in a few places, but it has definitely been improving. I've found the latest version to be much more stable and reliable, at least during the short time I've had it.
This is what happened to me when I bought a Nexus 5, and it was the final straw. I bought a cheap second hand iPhone 6S, and havn't looked back. I do miss the notification LED though, and the better clock/alarm functionality on Android.
I want a premium phone. I like good cameras, and big fat CPUs. So I've been using Samsung phones for a while. I currently have an S6, which I have been pretty happy with. But it has come to my attention that it has received its last update about 6 months ago. Samsung only sends updates for two years.
Having an internet-connected device that no longer gets patches? Seems like a terrible idea to me.
Apple supports their phones for 5 years. So that's the direction I'm currently looking.