I actually prefer the sensor on the back of the phone. I find it to be at least as convenient as on the power button, and with the power button placement, it frequently unlocks right after I just hit the power button to turn the screen off.

However, both of them are leaps and bounds better than the optical in-screen sensors that fucking blind you if try to use the phone somewhere dark. I had a phone with one of those for about 2 weeks before I returned it.