The Avatar Universe is by far the most peaceful out of all of them. At the end of the series all of the nations are on friendly terms so no wars. A normal person could actually live an exciting life as a bender or a simple one as a farmer and not risk getting killed every few weeks or so. I dunno about anyone else but that sounds pretty nice to me.
DBZ. At least when the Earth gets destroyed, they can just wish us back.
Except you'd occasionally hear Goku randomly talking to you telepathically about giving up your life force so you can make a spirit bomb. That would be irritating.
None, we already have enough problems in this Earth, don't need to worry on a daily basis for aliens, magical creatures and evil robots as well.
The Avatar universe has none of those. In fact it's quite a bit more peaceful than Earth is now.
Like what? Other than the Lion Turtle which poses no threat to anyone. Hell 99.9% of the population doesn't even know it exists.