How can anyone list the iPhone 4 as "worst" release? That was one of the best jumps in almost every aspect! Retina, 5MP and HD recording, LED, FrontCam, 512RAM, A4, Gyro, good battery and a really impressive design. Compared to that, the 4S was a disappointment. Better A5 but same RAM, Cam a little better, basic-level Siri and 100h less Standby time with overall inferior battery life.
I also regard the 6S as a bit overhyped here. It was basically what the 6 should have been from the beginning in terms of stability/bendgate, RAM and 4K. It still had an ugly camera bump and antenna stripes, pathetic 16GB of entry storage, no IP67, no OiS on the regular model and smaller batteries. The 7 was better in all those aspects + got stereo speakers, also the last iPhone with aluminum back rather than fragile and heavier glass. Since the headphone-jack never came back since then, I would regard the 7 as the much better device of its time. Chances are good it will still receive iOS15, unlike the 6S.
So imho the iPhone 4 and X as most striking new releases, 7 as most-balanced update, and the XR for earning respect as battery-monster. Honorable mentions for the 5S and 6S as solid (but also necessary) upgrades and the SE1 as last 4" phone. I love the current 12 series and my 12 Mini, not missing 120Hz at all, though a smaller notch and 128GB for all models would be nice, sure to come with the 12S/13.