I voted for 4/4S because it is the best in my opinion. The next best would be 5/5S/SE.
I never liked when they changed from those to current samsung or whatever Android phone look with rounded corners, which makes phone pretty much impossible to hold securely.
There is something magical in that style and I cannot really put my finger on what it is. Because when you look at the current SE side by side with current new style iPhones, it looks outdated but when you hold one or use it without seeing one of the new style phones at the same time there is this magic again. That does not happen other way around to me and new style phone just looks and feel cheap android/samsung style to me.
My dream iPhone would be 5/5S/SE sized 4/4S body phone (ss edge with glass on both sides) with X/XS like full body display without home button of course. That would make the phone pocketable sized and possible to use with one hand and glass back allows wireless charging.
Based on what the new iPad Pro looks like, I think we will see something like that in the future but probably on the larger X/XS style size.