I always get the newest phone available when my contract is renewed. Starting with the 4S, I have been on what I call the "S cycle" since November 2011. Upgraded to the 5S in November 2013. I hope the 6S+ is available this coming November when my contract is up for renewal.
On a side note, it is laughable that back in November 2011 I was intent on getting a BlackBerry 9930 but, at the last minute as I was standing the carrier store, I chose the iPhone 4S instead. A GREAT decision I have never regretted.