I gotta go with the original Raiders. Last Crusade is fun, Sean Connery is awesome, but in a way, that's part of the problem. Connery can't switch off the awesome, so it became Indiana Jones and His Dad's Crusade
Also, I don't share the hate many seem to have for Crystal Skull. Like the others, it's a fast-moving romp, no less unbelieveable than any of the others, and it tied up the series properly.