As far as I am concerned, the mini IS the flagship. I would never even consider buying one of the larger models, as I consider them to be subpar, unpleasant devices to carry and to use. I'd choose to carry no phone over having to carry a full-sized phone, they have become too large to be considered conveniently portable.
For me, the perfect smart phone would be the same size and shape as a credit card, edge-to-edge screen on all sides, and approximately 3mm thick. And it would run iOS of course.