Up until last week I had the S4, and before that the Desire HD, I've always gone with a top tier phone just purely that they are free on contract ( kind of ) so every year I'd upgrade. That was until I dropped and smashed the S4's screen, and had to re think the idea of a top tier phone.
I refuse to spend more than £100 with me being able to upgrade in about 7 months, so I went with the Lumia 625 Windows 8 phone, and it is the happiest I think I've been with a phone for a few years. It hasn't got stupid hand gesture use, or eye scroll, and all that gimicky stuff that probable 90% of people never use, but it has enough to keep me happy.
I especially like Cortana Microsoft's version of Seri for Apple, and it works great, I love the text feature where, when you get a text, Cortana says who sent it, and do you want me to read it or ignore it, after it's been read you can dictate a reply, or call that person or even delete. The only downside is with it being in beta, you have to set the phone region, to the states, but that's no biggie.
They come as standard with W8, but you can set up a dev account with Microsoft and install the W8.1 update, which makes it 100% better to use.