The one I have is called Mousewait. We were there the weekend after THanksgiving through mid December. It was really very accurate....certainly within minutes of what was posted (which remember can change at the blink of an eye). I believe that this one is generated by people at the park sending in what is shown on the signs outside the rides....I know I did it a couple of times when it was more than 5 minutes off. Remember, though that while I was there the wait times for most things were 15 minutes, with things like Space Mountain being under 30 minutes most times, and the longest the entire trip was Toy Story at 45 - 60 minute wait times.
We found it accurate enough that when we got off a ride we'd check it for things nearby to know which direction to walk and I don't remember ever thinking it lied to me, lol.
I decided to download that the morning we were to leave, so I didn't get around to looking into any others....but I think it would be fun to have more than one of the apps and play them against each other to see who is exactly right more of the time. Yeah, sometimes I get carried away with the fun of it all, lol.