- Will the majority of my target demographic have the Flash player? If you're sending a message to a specific audience, there are certain characteristics of your demographic that may make them more or less likely to have the most recent Flash player (or any Flash player at all) on their computers, and more or less likely to be willing to download it. If you think less than 50% of your audience will have the Flash player or will be willing to download it, then you may be better off using an animated GIF; while Flash requires a plugin to play, animated GIFs will automatically run in any browser.
- Does using Flash lower my file size significantly? 9 out of 10, the answer to this question will be "yes". With simple graphics, vector-traced SWF files are almost always going to be smaller than sequences GIFs because of the way the images are stored and rendered. However, if your graphics aren't simple--say if you're importing detailed bitmap artwork into Flash and leaving it as a raster image rather than converting it to a vector image--it's possible that you may end up breaking even or even coming up with a smaller file using an optimized GIF.
- Am I using audio? This is another major dealbreaker, like the requirement for user input. If you're using audio, you'll need to stay in SWF format, as animated GIFs are image-only. However, if you're not using audio, then the SWF format isn't really necessary, as both the SWF and GIF will accomplish the same ends in playing the soundless animation.
With those four major questions in mind you should be able to weigh the pros and cons of using SWFs or animated GIFs based on your specific needs and specific purposes.
