I almost always power the boat on, but everything depends on the circumstances. Steepness and composition of the ramp, wind, current and wake thrown up by other boats can all make it harder to load either way.

Until you are totally comfortable with your boat, winching is definitely safer. My sister-in-law was having real trouble loading an I/O on a river with a particularly fast current. She gunned it at the wrong moment and put the boat up sideways on the trailer, creasing one fender on the trailer and scraping off some gel coat on the boat. Inboards are even harder to steer, so it takes a lot of practice.

To all you haters: just because you power on doesn't mean you are going max throttle for 10 seconds. I line up the boat and drift in, then nudge the throttle to push the last bit onto the trailer and engage the boat buddy. When we unload we stop just before the winch is over the water, my buddy/driver unhooks us, backs in the rest of the way and does a little short stop, easing the boat off the trailer. He's already pulling out before I even start the motor.

All launches are going to develop a mound or ridge behind the ramp. Most places will dredge it out every few years. This happens because of power loading *and* unloading and it's inevitable. If you feel more comfortable winching that's totally fine: it's your very expensive toy and you want to take care of it. But don't condemn power loading simply because some people don't know how to do it.