Assuming someone coming into the market fresh with no prior investment in either ecosystem:
iPhone: "just works", but its quite a closed system, with restrictions in what you can do (assuming you don't jailbreak it). You'll also pay a premium in "Brand tax", and be tied into the iPhone ecosystem.
Galaxy s7: much more open - no real restrictions on 3rd party apps, however this does come with some downsides; fragmentation, apps may not be optimised properly, some apps may not work on your particular device, and some may have malicious code. The Samsung phones in particular also suffer from "Brand tax", however the benefit of Android is, in 2-3 years when you want to change phone, you're not tied into a particular brand/model