Hi There!
Congratulations on your visit to Zion! I spend time there each summer as a canyoneering guide. I prefer the Watchman campground as well. The park can get very busy and the reservation is a good thing to have. I prefer the sites that are all the way in the back next to the Virgin River.
There are so many amazing places to visit in the park. Just know your skill level and don't go up Angel's Landing if you are not in great shape or are afraid of heights. Weeping Rock is a pretty and easy warm up hike. I recommend riding the shuttle all the way through at first to get an idea of what you might want to go back to.
Have fun!
