With regards to other options, the phones come out more or less even. There isn’t much point in comparing the hardware specifications for things like the processor, RAM and GPU, as both phones are running entirely different operating systems with different ecosystems.
What’s more, iOS is designed specifically to run on Apple’s devices, unlike Android which has to support a much wider range of hardware. This gives Apple some advantage with regards to the phone’s performance, but it’s not that fair to claim that the iPhone 6s is “better”.
And on the other hand, even though Apple are known for an elegant approach to their designs and they generally make light, stylish devices, the iPhone 6s Plus is actually heavier and larger than the Galaxy S6, making the latter a better choice for those who like a more compact device.
In the end, opinions seem to be leaning towards the Galaxy S6, both from critics as well as fans, which is a bit strange as Apple usually have a lot more support after making a major announcement. Some have been speculating that the company has been losing their edge lately and their releases have been getting far less impressive than they used to be, and there might actually be some truth to that, looking at their recent performance.