Before I had my current phone, I had the Samsung Galaxy S5 (which I dropped and ruined the screen lmao) For me, the biggest difference between my current iPhone 6S and my old phone was the design of the homepage layout. I don't know the official name but basically where the apps and stuff are.
I think the iPhone 6S's camera quality is better than the S5's. I'm pretty simple in terms of what I need in a phone. Something I can use to call people, text people, download social media apps for, easy to transfer photos and videos + easy to download music. Apple's iTunes system where you'd have to plug in your phone to transfer music was so bothersome, but they have Apple Music now so life's a bit easier. I also like the AirDrop function as it allows me to transfer files between my laptop and phone, or my phone and my friends' phones.
For cons, the maintenance costs are pretty scary. If I ever majorly crack my screen, I doubt I'd go to the Apple store to get it fixed tbh. It is SO expensive!!! Also, the battery drains pretty quickly too, even with Bluetooth and Wi-Fi turned off.