Animated GIF's are a great way to make your Flash animations accessible to those who don't have the Flash plugin, or in areas where you can't upload Flash SWF's. It's easy to publish animated GIF's from Flash
GIF images are more suitable for this purpose as they require less bandwidth and load quickly. Flash images affect loading speed considerably and make sites slower.
hi, I will give my vote to Flash because it has good features and animations to create interactive website header and if you want to have business over web then you must create your product or service banners in GIF because it possess small image size with animated effects.
Flash is much better, but overall I'm not using, as it only consumes extra bandwidth and if you are looking to build a great website is not really necessary.
GIF images are a preferred choice for most when developing websites as they require less bandwidth and load quickly. Flash images on the other hand decrease the efficiency of a website significantly by decreasing loading speed and making the sight run sluggishly.