I still linger on a basic 6 and probably will until the battery life becomes intolerable. I buy outright so I like to get the milage of a handset. I have an SE from the mothership which I like (it's the chunkier iPhone 4 size) from a size perspective. I'm not sure I'd go plus, I'd image you've have to be careful not to vasectomize yourself if you stuffed one in your pocket and the screen size hovers between various impracticalities – it's neither especially portable nor large enough to be genuinely useful as a non-portable device.
It has 64GB, I like to keep all my tunes, books, etc. on it and not rely on data connections.
Horse for courses, though. I'm a pretty basic user – phone, texts, email, maps and GPS, book reading and browsing. I don't have, want, or need a bazillion apps and I can't be arsed playing games as there are too many books in the world waiting to be read.