I'm surprised the most popular wasn't the iPhone 5. Loads of people seemed to have them...purely based on my own observations of course.
The 6S doesn't seem to be as popular. I hardly know of anyone who has one.
You can attribute that to Apple and their unhealthy obession with the iPhone 4/4s. Rather than move the 5 down when they launched the 5s like they did the 4s when they launched the 5, they repackaged the 5 with slightly better internals and a plastic case (iPhone 5c). At the same time, they did not discontinue the 4s.
But they most certainly cut off the iPhone 5. After only one year of sales.
Yeah, having bought a 5 on launch day as my very first full on Apple iPhone purchase - I'm still bitter about that.