Some of the stats reports that we provide you with are graphs. These can be displayed either as static GIF images or as a Flash objects. Flash contains a bit more information and is interactive but is slower to load. The image format on the other hand loads very fast and is used by default.
We suggest that you try the Flash setting then go load a report like 'Traffic over time > per day' and see if you like it. If you don't, go back to the Control Panel and change the setting back.