For me
1. 6S/6S Plus - Last iPhone where you could literally feel the difference in performance coming from the previous generation. Doubling of ram to 2gb gave this iPhone insane longevity, granting relevance even till today.
2. iPhone XR - New form factor, new authentication system, new gestures, more vertically space, popping colours all at a reasonable price. The iPhone for the masses, that had a bigger screen, more battery life and better low light portraits compared to it’s more expensive sibling the iPhone XS. The success of this iPhone is probably the reason we now have so many colour options. The iPhone that made iPhones “fun”.
3. iPhone 13 Pro Max - This is the everything including kitchen sink variation of the iPhone. A culmination of everything that power users have been craving in pass generations lumped into a single iPhone. Starting with an enhanced version of the chipset featuring an upgraded version of the GPU compared to the regular iPhones, the first time such a distinction has been made between the Pro and regular models. The most improved camera hardware in a single generation, also the most versatile. The biggest, brightest screen on an iPhone along with 120Hz ProMotion, it’s the first iPhone that feels more fluid in a single generation since the 6S, mainly due to the improved display tech rather than pure performance improvements. The biggest battery ever in an iPhone boosting true yet unbelievable all day battery life. Also the first iPhone to feature 1TB of storage space. Workhorse of an iPhone, and go to iPhone for any iPhone power enthusiast.