It’s been a while since I’ve done full-time Android development, so take my views with a pinch of salt! The platforms share plenty of similarities, like the view lifecycle, and both now have great modern languages to build with: Swift for iOS and Kotlin for Android.
For all that iOS developers like to complain about Xcode (iOS IDE), Apple really do invest a great deal in tooling to help developers create great UIs. Interface Builder is a great tool for which Android Studio doesn’t (yet) really have a match.
Apple’s documentation is also generally excellent. The flip-side is that iOS is closed-source, whereas with Android you can dive really deep when diagnosing problems, even if the documentation is sometimes not as thorough.
I personally get more enjoyment from developing on iOS, but perhaps one day I’ll switch allegiance again
This one’s tough! Lately Apple’s focus has been more towards readying the software and hardware support for AR (Augmented Reality). Whilst that’s important for them, it’s not so relevant for utility apps like Monzo, and I don’t believe in using a technology for the sake of new and shiny.
I’d personally love to spend more time on some of the older technologies that don’t make the headlines: things like VoiceOver support, haptic feedback, rich push notifications, etc. The combination of these sorts of technologies lead to a much richer, more magical experience than any “big bang” from Apple
It’s a world of pure imagination 
