I have a 12 mini. I don't use my phone for much, it's just a tool for reading websites/email/maps/texts/music/weather and sometimes videos. I use the camera occasionally but just as a tool for information, not really to take nice pictures of places.
To me it boils down to a question of is the phone your main 'computer'... if you live on your phone a bigger screen seems a natural fit. But if it's more utilitarian and you like to do more 'computery' things on laptop/desktop or tablet... the mini is a great fit.
How some people use their phone, I use my MacBook Air... I carry it with me everywhere and have it ready to go for anything more advanced than looking up the weather. I do 90% of my text messages on it.
For me, the mini is the best it'll ever be for a phone I guess. I think the 6 size is uncomfortable to hold but manageable, and anything bigger than that is silly. I kinda get the bigger phones though, if you are resigned to it being unwieldy you might as well get it as large as possible. They should just put grips on the thing like a video game controller...
My primary reason for a mini is because I get around by bicycle, and I want as small a device as possible in my pocket. Going way back I had a Samsung S3... which I think is about the same size as a iPhone 6... and that felt like a giant slab in pocket biking around... I can't imagine a bigger one.
Also I'm a person of a bygone time where the best tech is always in the smallest design possible.
I know the mini is way more phone than I need right now, and just plan to use it until Apple stop supporting it. I'll either perpetually get battery replacements or get a lightly used 13 mini.