Well, looks like I'm about the only one that went the other way, from a Samsung S9 to the Pixel 3. Despite the great screen and speed of the S9, got tired of all the millions of settings, Bixby that kept turning itself on again after following "How to Completely Turn off Bixby" articles a few times

, irregular updates, all the Samsung apps that duplicate Google functionality (including Bixby) that I couldn't remove. On the other hand, the Pixel 3 has a great screen and is fast (where it counts for me), and will have the security of regular updates over time. And I have a lot more control over the apps that are on my phone.
As far as customization goes, for me the biggest thing that immediately struck me was the lame Pixel launcher. I don't use the Google search widget on my home page or need the day of the week and current temperature on my home screen every time I open the phone. So I went to the Nova launcher, and have a very nice minimalistic arrangements of icons on my two home screens. With the "dock" integrated into that rather than separated by a box or line or whatever. Anyways, Android customizations are available to anyone, you don't need to be an Android guru to figure out how to do these things. You just need to have an idea of where you're going, and there's lots of information on the internet on how to get there with Android.
Speedwise, I don't stream video media or play speed games on my phone, or do much with my phone that would leverage the raw speed of the "Bionic" iPhone processor, so that really doesn't matter to me. My apps open quickly and operate quickly and smoothly on the Pixel 3, that's what I care about. These "speed tests" where apps are opened and closed one after another, either manually or automated, are meaningless to me. What matters to me is that what I do with my phone works well. And faster than any phone that I've had.
So far, the Pixel 3 is the sweet spot for me, really enjoying it. I had the original Pixel, and liked that, followed by an iPhone 8, which I also liked. And then the Samsung S9, where I found that Samsung and I have different ideas about what's important on a phone, I'm looking for quality, Samsung offers quantity without a reason for it. I find that I love the larger screen on the Pixel 3, and the fact that I can set my phone up the way that I want it, not how Apple wants it. Battery consumption/life is about the same for me as the iPhones (and S9) that I've had, no problems there.
Just really enjoying using the Pixel 3. Haven't gotten into the camera much yet, but looking forward to playing with that as well.