With Big Thunder and Space Mountain down, I suspect Matterhorn is busier than ever. But my past experience has been that the line is usually shorter on the left side as you face the entrance to the ride (i.e. the Tomorrowland side is shorter). This is especially true early in the morning since the tendancy is for guests to come from the Main Street/Castle area. Also, the line during some parades may seem longer, but will move twice as fast. This is because both sides of the ride will usually be operating even when the line on the Fanstasyland side is closed (for the parade).