Like a few others, my personal phone is a 4S, which is just out of contract, but I think is the perfect size. Don't want or need a bigger screen/phone. It was my first iphone, but I really like the interface. Downsides are the lack of 4G (real problem in inner Melbourne using Optus!), poor battery life and it's starting to get a little slow (running iOS 7.0.4).
My work phone is a Nokia Lumia 635 windows phone, which so far I'm very impressed with (only had it a week) - looks a lot like an iPhone and windows not that different from iOS. Think it has a 4.5" screen, which is just too big, but doesn't have as much top and bottom border as 4S, so not that much bigger. Had a Samsung Galaxy Ace 3 for a couple of months prior to the Nokia - biggest piece of cough I've ever seen/used! Didn't like Android (at least Samsung's version) at all. Impossible to type messages on the terrible keyboard and I don't have large fingers! Never been a fan of Samsung products though.
Might just ditch my personal phone and rely on work phone!