It all depends on too many variables to give a complete answer. We use the campground wifi quite a lot. But we tend to travel in early spring or early fall, so there are generally speaking, fewer people staying in the campground. We also tend to make use of wifi in the morning, or early afternoon, and usually find the service usable. Trying to use most campground wifi any time after 5:00 in the afternoon is usually a wasted effort.
If you need consistent internet connection you pretty much will have to supply your own. What you choose will depend on how much data you plan to use, and how fast you need it to be.