50/50. We use it when it's working to keep our cell plan usage under control.
We have noticed a clear pattern in many parks, where it is quite fast on weekdays but friday afternoon rolls around and it slows right down, sometimes becoming unusable.
It's a moving target though. Campgrounds are getting better. They are adding repeaters for better coverage and getting higher speed connections but expectations are also going up. It used to be a small percentage of campers used the wifi and usually just to check email and a few websites. Now, probably more like 70-90% use it and many are streaming movies.
If you NEED a connection, plan on your cell plan and wifi is a bonus.