I love South Campground when I go to Zion. Recently, they switched over from First Come First Serve to a 2 week reservation system ($20/night) so be aware of this when you want to go. You can check for cancellations, which is how I got in the last time at the last minute. You can't beat the views at sunset, you get to look up at the watchmen and be in awe. It is worth one morning doing the Watchman overlook trail, and also pulling your camping chair into the virgin river behind the campground after a day of hiking and walking.