Experience is great since I pretty much own every Google phone and also every Galaxy phone lol.
The time when I miss Google phone is when new OS rolls out for example android O rolls out. That is the time I switch to the new Pixel. If you really care about OS updates then stick with Google. On the other hand Galaxy phones come filled with features, you can also turn them to pretty much look like stock Android if you want. At least on the S8+ it's screaming fast and hopefully doesn't lag few months down the line like most phones do. Some people will say their Galaxy S4 runs still like new

but it's all depends on individual if you can see lag, stutters etc. Overall at those point you will be really happy with S8, but I don't know after 6 months if it'll the same.