I have used both. If you are running late (like coming from MCO) or not sure where you want to eat until you get there, then we use OpenTable. We use OpenTable a lot for Raglan Road. Several times, we have walked up and been told the wait is 60 - 90 minutes and if the bar is full, then we look at OpenTable and majority of the time get a table in 15 - 20 minutes. OpenTable works best for restaurants at DS or throughout different resorts but not for the parks.