As per our opinion,
Choose the iPhone 7 for the sheer performance, a very well equipped camera, top notch build quality and the seamless iOS ecosystem.
The S8 has the better camera, better screen and better security features. Though if you are someone who has performance as the top priority, the iPhone will suit you better.
The Pixel is quite old now and if you want to buy a new phone which is a Pixel, wait for the Pixel 2 which will come out in November.
Personally We would suggest you to buy Samsung Galaxy S8. No regrets whatsoever. This phone has a futuristic design.
The iPhone looks very old already when compared side to side. Also the software is greatly improved and UI is very light and smooth. No unwanted bloat-wares and many useful functions.
The fingerprint scanner is the only downside but you’ll get used to it. Iris scanner is fast. The display is currently the best mobile display! Camera performance is really good.
Low light is fantastic. Just that we were expecting Qualcomm Snapdragon 835 SOC But it’s with Exynos 8895 processor. It’s Still good!
Pixel takes slightly better natural pictures in daylight but not much of a difference. All in all this phone is an all rounder and must buy!
Overall, Samsung Would be the pick!