Lol...
6 chances at a good Android phone & never once got one above the GS3????
Color me confused. Umm... That's probably the main reason you keep switching, I couldn't hazard why it took you a half dozen tries... perhaps addicted to the "thrill" of buying & selling on craigslist? Owning VERY old kit & getting to pretend like it's new? At any rate, yes... a GS3 is probably like 20% the phone a 5S is... However, an actual "Google" phone like Nexus 5, offers more like a 90% similar experience to iOS in terms of fluidity, ability to handle multiple apps without choking, etc.
I suggest if you're going to continue to bounce back & forth- treat yourself, don't cheat yourself! Try a current gen Android phone next go, perhaps without an added UI layer to considerably slow it down.
I prefer iPhone myself, but if I were to go back to Android.. would not even briefly consider a handset without the word "Nexus" in the name.