I'm very confused... You're going to be carrying two phones at all times? Or if you're thinking you'll just bring the 11 when you need a better camera; Why not just get a DSLR instead of a phone, when a camera is what you really want from that second device, not a phone?
Frankly phones don't really excite me very much. The iPhone 4s probably impressed me the most at the time, but its memory is tainted by it getting so slow at the end of its life. But I guess I've always liked the refined S models the best; 3GS, 4S, 5S, 6S, 8, SE. The 8 was basically an S model in my book. But when it comes to phones I really just want an appliance that just works. When it comes to excitement and joy I look mostly to the Mac, but in recent times also the Apple Watch. The AppleWatch is also very much an appliance device, but it's a rather magical experience that even after having had mine for a good bit over a year, almost 2, still feels fresh and exciting all the time. And the Mac is just such an important product to me. Every single day I love my Mac - and I need my Mac. I could not do what I do without a computer running macOS frankly. Not as efficiently anyway. And when it comes to the Mac your question is much more interesting to me - Macs that have very special places in my heart are the G4 iMac, the MacBook Pro 1,1 - Frankly the design of the 1.1 holds up to this day, with slimmer bezels than the Retina generation, and absolutely fabulous attention to detail with things like the breathing light. And the G4 Cube, while a bit of a flop is still a marvel. I've never owned one, but the classic cheese grater is also an unavoidable juggernaut of Mac designs that I've many times drooled over in Apple Stores.
In essence what I'm saying is that an iPhone is just an iPhone. It's a great phone, but it's not exciting to me. But the Mac is the most exciting thing in all of technology. I need it for work, but it's more than a device of need. Every interaction with a Mac is joyful compared to a similar interaction with any other device. A Mac is efficient, flexible and fun. It's the hub of creation and recreation. And it just has the more interesting designs, especially in the PowerPC days, but also still today.
Sorry for the massive tangent away from the point of the thread, but yeah. Answer to your question overall would probably be the 5S actually. Just cause it felt solid the longest I guess