iPhones are amazing pieces of technology. Generally speaking; they "just work" with very little fuss. Although, some may argue they have become more and more finicky the further we get from Steve Jobs obsessive personality leading that company (that's actually more of a compliment than jab).
iPhones also can be counted upon to be upper tier with features and specs. You just can't hardly make a mistake picking your model.
Now all that said; I moved away from iPhone after the iPhone 6. I am personally done chasing the highest specs available at a premium price.
The phone evolution curve, IMO, is flattening. Every new device is slightly better, but rarely revolutionary. Look at the IPhone X. Its not much different from the Samsung Galaxy line. In fact, many of the upgrades in the X were launched in April on the S8.
So like PC's years ago, there are a lot of good choices out there and it's now a matter of "what is important to you".
Also, like PC's, you are starting to see high end performers at better price points.
As example; I am using a Blackberry Keyone. Typed communications are important to me so I wanted the keyboard. I also wanted all day battery life. The phone has good specs, but not the latest generation, at a price point of $550. Might not be as cool as the iPhone X, but it fits what I value.