I have upgraded to an iPhone 6s one month ago. My main issue with my previous phone, an iPhone 5s, was the limited storage that it had. I indulged and got 128 GB storage. With all the space that I now had, I started taking many crisp, nice photos and enjoyed my larger screen. It was fun to just address Siri and got her activated.
Then I realized that I was having one issue over and over. As I tried to lock my phone, I was only increasing its volume. The volume up button is on the opposite side of the lock/ on / off button. I was holding the phone with one hand, my thumb on the lock button and my index finger on the volume up button. When I applied pressure on the the lock button, physics would come into play and I would need to apply pressure on the other side to keep the phone in place. At times, I increased the volume. At times, nothing happened. Sometimes, I was able to lock the phone. In terms of usability, the success rate was really low!
I am not the only one who is having this problem. Other people have voiced similar opinions, like here and here. Even though the second post says it is impossible to leave the button on top as it used to be due to its size, I would rather have it back there. It might be hard to reach it but at least I would get what I want: locking the phone.