MacAddress have just released a video where they go through the effort of testing every iPhone camera*, so they could see how it has evolved over the many years. It's pretty amazing to see what the cameras are capable of now compared to the original iPhone. (Although I'd still like to see a little less processing on current iPhones).
One thing they quickly rushed over in the video was that the 3GS is apparently gaining some popularity due to the style of photos that the 3MP camera produces.
PetaPixel published an article "TikTokers are Obsessing Over the iPhone 3GS Camera from 2009" which is also a fascinating read. After looking at the comparisons in that piece, I have to admit, photos taken on the 3GS do have a nice retro/film/nostalgic look to them, that I definitely find pleasing. I think I may have an old 3GS somewhere in my house, so I might need to experiment with that at some point.
*For reasons they explain in the video, this didn't include an iPhone 3G or 5.