I have never had an Android phone last more than 3 years. Most of them were sluggish or degrading after only 18 months. I'm 23 months in on my first iPhone and it feels as fast as the day I got it. I can't recall ever experiencing battery life anxiety either. I have friends that have used their iPhones for 5-6 years with no problems.

The upfront cost is higher but you can expect a much longer service life and the resale value is higher if you still feel the need the newest model on shorter timeframes.