I had a pixel and it was a solid phone. But nothing wow to me. I like to try different phones so after a while I like something new. I really missed Samsung pay and I use it for everything so that was my main reason to switch. The s8 does have a much louder speaker and the water resistance was also welcome.
The pixel is still a good phone but to me felt like a rushed product and not fully polished. Almost as if I was a tester to see how it would run with the big sellers ( Samsung, Apple). I'm glad to see they are putting the finishing polish on the next version, ( water resistance, edge screen, camera.) But like I said I enjoy jumping around phones.
They all have their selling points and they all have their downsides. These days phones are all pretty much on the same par as flagships go. The pixel was a solid daily driver with fast updates and a great camera. Just not with all the bells and whistles that Samsung has. If you keep these in mind I think you'd be happy with either device. There will always be something bigger and better a few months later anyway. So no, I don't regret switching.