The Samsung Galaxy S9 is a much better phone as it gives better specifications at a similar price.
Processor: The Samsung Galaxy S9 comes with the Samsung Exynos 9 Octa 9810 processor whereas the iPhone 7 Plus comes with the Apple A10 Fusion APL1024 processor.
Camera: The Samsung Galaxy S9 has a camera of 12 MP with F2.4 - F1.5 aperture whereas the iPhone 7 Plus has a camera of 12 MP + 12 MP with F1.8 aperture.
Check Full Comparison iPhone 7 Plus and Samsung Galaxy S9
Though both the device offers the same 2.3 GHz Samsung Exynos 9 Octa 9810 processor, But the Performance of Samsung Galaxy S9 Plus is much better processor.in comparison to Samsung Galaxy S9 and It can be explained by comparing the benchmark score of the two devices.
Also Samsung Galaxy S9 plus comes with a better 6.2-inch screen size in comparison to the 5.8-inch screen in Samsung Galaxy S9. Bigger screen size always gives a better smartphone experience as you can have much clarity and a much better movie watching experience on your device.
Now it is all clear that Samsung Galaxy S9 Plus is a better device in terms of overall specs and performance.
To check all the other details, you can visit the following link Samsung Galaxy S9 Plus vs Samsung Galaxy S9