iPhone is a great choice and is definitely better than most Android options. I have always used an iPhone and Mac, so I am very familiar with how they work. Even though switching to GOS wasn't difficult, I still have my iPhone just in case I do need to switch back to it.
Advanced Data Protection (ADP) definitely makes the iPhone and Apple a lot more enticing than Google. The fact that a Big Tech company actually offers the option to end-to-end encrypt most of your data on their servers is great, and I hope more Big Tech like Google and Microsoft imitate that. The same can be said with Lockdown Mode; if Google and Microsoft had a similar feature, it would make their devices much more secure.
The iPhone was always recommended to journalists and others who needed strong security because of their jobs for many years. While the iPhone is much better than most Android OEMs, the differences between it and stock Google Pixel in terms of security aren't that much as Android has improved a lot. But I'd probably still recommend the iPhone because of ADP and Lockdown Mode. My recommendations from best to least in terms of security:
- GrapheneOS (best security)
- iPhone (great security + option to harden via Lockdown Mode + ADP)
- Stock Pixel (great security)
- All other Android OEMs
I do recommend an iPhone or stock Pixel to everyone I know. I know not everyone would want to flash an aftermarket OS onto their phone, so these two are the next best options for a secure phone.