I went a roundabout way to get to iOS. I had only every had a Windows Phone as my daily driver since switching over to smartphones around 2012. First I was on WP7 and then 8, 8.1, and Windows Mobile 10.
So last year I decided to switch and I went with Android. A primary concern was updates to the OS and how frequently the OS came with junkware forced on you by various OEMs. I went with a brand new Nexus 6P with 64GB of storage. I worked well enough and I could customize it. I used MS' Arrow Launcher and tried others. I used all the MS services on it I could. It did not take long for it to get a bit flaky and for the rather large battery to get drained. Lots of rogue apps that could just eat up your CPU, memory, and battery. The need to be looking at what was sitting in memory and having an app to try to shut down stuff was a major pain.
In November I picked up an iPad Pro 9.7. I have long been an Apple critic (though I was a Mac user from 2002-2008 and left for some very specific issues), but the iPad is the best tablet when it comes to just being a tablet. I found I enjoyed how easy it was to use for light tasks. I still used my Windows desktop and my Android phone quite a but, but the iPad was always great for a bit bigger screen with better speakers to do some browsing, reading, etc on and it was always ready to go at a moment's notice.
So in February of this year I decided to exit Android's world and get an iPhone 7 Plus with 128GB of storage. I've been very impressed with the build quality, memory management, battery life, and updates. They've updated the file system while I've had the phone and I've had no issues. No resets. The built in multi-factor authentication works great (as does MS').
Apple has a GREAT app for switching from Android that took care of transferring contacts, text messages, and downloading all my apps in the store pretty seamlessly. The iCloud backup is also very good and worth the $0.99 I decided to pay per month for 50GB (and I still backup all my photos in OneDrive as well as Google Photos).
Like any phone, the battery will drain if you watch video, etc. I did have a day several months in where I streamed music to a BT speaker for about 8 hours and the phone went from 100% to 85%. I checked texts and FB a few times during that period, but I was working and not using it for much other than streaming. On days where I'm busy and it sits in my pocket, it pretty much sips the battery. It's not odd to look at my phone 10 hours after it has been taken off the charger and see it at 90%. Granted, that's a light use day, but the Nexus would be done to 60% or worse on a similar day.
I did use Microsoft's WordFlow keyboard for awhile, but that got discontinued and they are going to put many of its features into Swiftkey, so I switched back to that. It works well.
All the apps I had on Android function more reliably and use less power, CPU, and memory on the iPhone than their Android counterparts. Apps have crashed VERY rarely compared to Android. iOS has never mysteriously rebooted like Android was prone to do (I ran both M and N).
With the iPhone, the phone is pretty much transparent. It just works. It doesn't cause problems. Every app known to man is available. You have every choice imaginable for cases. Applecare+ is excellent if you decide to get it. And Apple supports their phones longer than anyone else. The iPhone 5 only recently stopped receiving updates FOUR YEARS after launch because it was not 64 bit. It's not unreasonable to assume that a new iPhone 7 could be supported for 4-5 years from now. It may not be quite as fast or power efficient, but Apple is likely to supply iOS updates for many years down the road. And if the battery gets less impressive during the first two years and you do have Applecare+, Apple will replace it for free. Outside of that time, they have a FLAT $79 fee to replace the battery with a new one.
So while people may complain about the cost of an iPhone, truth is that Apple supports them better than any other phone OEM. Updates are more reliable than anyone else. Security is better. iOS forces developers to not take shortcuts they can take in Android.
I'm much, much happier with an iPhone than I was with Android. I loved Windows a lot, but the iPhone has so much more to offer. Windows Phone could have achieved something similar without some missteps and if they could have gotten the public onboard, but the iPhone is really the only good choice in smartphones at this point. Android is so hit or miss and is a big pile of frustration quite often.