We stayed at both in March. Watchman was by far our favorite. We felt like we were emerged in the canyon more. Easy walk to trailheads,visitor center and shuttles. The other campground was under much construction, short staffed, and not overly friendly. But they do have a shower. You get a few tokens per guest to take a quick shower.

We’ve only been to private one just outside the gate. Great location but very tight spacing and campfires can mean wood smoke in your windows. Also, we had a problem with someone in a nearby space smoking marijuana outside. Marijuana is illegal in Utah and some people like me have a bad reaction to it. I put in a complaint and the office sent someone out to put a stop to it. The very close spacing makes any kind of smoke a potential problem. Otherwise a nice park.

IF you could get 3-4 nights in Watchman, I'd take it in a heartbeat. Having stayed in both, on the same trip, Watchman is so MUCH better. The only positive to the private campground is the showers, and you can find other places that will let you shower.

I didn't stay in both, but I can say that if you own or have the means to rent e-bikes then staying here is a great choice. You can't really drive around inside the main part of Zion, so your choices are shuttle bus or biking and I for one loved biking through the canyon as one of my top 5 experiences.

Go with watchman. We would next time.