I was using an iPhone 4 until that died,then since the iPhone went to big screens I got a Sony Xperia Z1 compact. It's still a big phone at 4.3", but it's a better size than the iPhone 6.
I want a 4 inch screen as well but they aren't going to release one with the 6S just cause it's going to require a redesign of the phone. they can only do it with a phone that's still in development. hopefully it'll come out with the iphone 7.