I think it depends a lot on how heavily your phone gets used, and how often the battery discharges deeply and is recharged. These batteries have a certain number of charge cycles before they start to lose capacity, so the more often they're fully discharged the faster they'll start to fade. To maximize battery life, don't let the battery get below 25%. Frequent short charges, to keep it above 50%, are better than letting the batter discharge fully.
Heat is also the enemy of batteries. Fast charging generates a lot of heat. Charging off the stock 700mA charger, or a USB port, is better for the battery that a high amperage rapid charger. Running apps that heat the phone up (like using GPS for long periods, and especially using GPS while charging) will shorten battery life, too.
In the end, just be glad you have an interchangeable battery and can get an inexpensive replacement. Just think how the htc One owners are going to feel when their batteries start fading.