The 2016 iPhone isn't officially out yet. So we don't know how it's going to actually be like.
To me, the iPhone and the Samsung Galaxy devices are great phones, but they have different philosophies.
The iPhone is focused on delivering a fast, smooth experience while offering the basics, without anything too fancy or stuff that users may consider "gimmicky". You won't find super-extreme-ultra killer features on the iPhone (though NVMe storage on the 6s is considered pretty killer for me, along with 3D Touch, but YMMV), but it offers a pretty consistent experience. The Galaxy devices are focused on giving the user as much features as possible, such as multi-window, S Pen stuff on the Note, edge panels on the Edge devices (Note Edge, S6 edge/edge+, S7 edge, Note7), Samsung Pay and others. This means that the Galaxy devices can do much more than what an iPhone could right out of the box. However, you won't find iPhone or Nexus-beating performance here, but Samsung has cleaned up their software quite nicely in recent times, so while it's not iPhone-fast, it is still as fast as a lot of flagship devices released this year, and in the real-world, you'll probably not notice a difference. My Note has been a pretty fast performer, on par with other flagships released in 2016 in the real-world.
Naturally, this comes down to personal preference. Do you want a consistently fast and fluid experience and don't care about the extras while also caring about a really long software-update timelines? Go with the iPhone. If you want more features, see yourself using them, and find that they really improve the user experience, go with the Galaxy devices. Ecosystem also plays a role here.