Far too subjective, you could go on many things, specs, units sold, battery life... etc etc etc.
Much better you tell us what your best phone was for you and why. A lot more interesting.
For me my all time favourite devices from these years only,
2007 the Nokia N95. I still have that little Symbian Brick. It still works as well.
2009 the Nokia N900, a weird Linux (Maemo 5 -Freemantle, a fork of Debian) tablet with phone functionality It was "root" by default and you could program it from terminal directly. The best mobile browser in the form of "Micro B" I have ever seen, and I include today's efforts in that. Unfinished (it didn't even support MMS messaging natively), buggy, but stunning, truly stunning. I actually got it to boot Windows 95. A totally useless exercise; it took nearly an hour to get to desktop, but it did it. It had true multitasking, back in 2009. Still have this one as well and it still works. The battery lasts about half an hour though from full these days.
2011 (funny, this seems like every other year) Samsung galaxy S2 - my first Android phone. It was like coming home to Symbian and was what that doomed OS should have become.
2012 - an honourable mention to the Samsung Galaxy S3. loved it and modded it to pieces.
2013 Samsung Galaxy Note 3. Curates egg, flawed, massive, but lovely with it. still used daily by a work colleague who bought it from me.
That's it, I'm currently rocking a Samsung galaxy S6 edge. It is more than fine,it is stunningly superb. TouchWiz is no longer a swear word, and even the added "features" are fewer and easy to get rid of in some cases; and it is for all intents and purposes as good in Marshmallow guise as it's newer younger flagship the S7 edge. I think the age of huge improvements in the "flagship" side of things is at an end. Indeed the more esoteric manufacturers from China are producing some fabulous devices for less than half a "flagship" cost.
So there you go, not one overpriced locked up fruity phone mentioned.
In all seriousness the iPhone 6 is a very, very nice device (I have an Apple mad friend, we upgrade our devices at roughly the same time every two years and have since 2012 swapped devices (and used as if from new) for a week, over Christmas usually. Last Christmas we could have happily swapped our "6" devices, he however struggles to get an Android device to work with his Apple centred home, with it's Mac, iPads and Apple TV, not unsurprisingly.